The session limit is only for calls an rtpengine is responsible for.
Foreign calls (coming in via redis notification) are not counted as
long as the rtpengine is not responsible for those calls.
At least that means that the limit may exceed if the calls the rtpengine
is responsible for plus the former foreign calls are greater than the limit.
This will happen suddenly when the rtpengine becomes responsible for the
foreign calls.

closes #119

Change-Id: I9c5f3a560088ffb04c02e1b229a2616132a506e6

Currently, every rtpengine will subscribe to redis-keyspace notification
so it will receive a notification when an call is inserted. If the call
is not already handeled by the rtpengine, the call will be restored.

The reason for this is to have in-place redundancy. Imagine you have
multiple rtpengines running, eachone will have all calls of the others.
When one rtpengine fails somehow, infrastructure guys use BGP in order to
'move' the IP address from one rtpengine to another. Thisone can handle
the new calls instantly since they're already recovered by
redis-notification feature.

Next step is internally identify those calls in order to prevent some
timers to delete the calls where no RTP flows. Second will be
something we call 'partitioning'. It means that the subscription
to a redis notify will only be for the keyspace a dedicated rtpengine
writes to. This leads to the point that you can make redundancy groups
(partitions) of the rtpengines.

Change-Id: I8383742ec11983d82ab4e2e92f1e20cbda798d71

This brings master up to date with branch `rfuchs/socket-rework` at
commit `b1bcc096b7`. The branches have diverged too much for a proper
merge, so this is a manual (squashed) merge.

The old master before this merge can be found in branch
`old-master-before-socket-rework` (commit `82199216b2`).

This is a complete rewrite of all socket handling routines. The most
important functional change is that sockets aren't indiscriminately
bound to INADDR_ANY (or rather in6addr_any), but instead are always
bound to their respective local interface address and with the correct
address family.

Side effects of this are that in multi-homed environments, multiple
sockets must be opened (one per interface address and family) which must
be taken into account when considering RLIMIT_NOFILE values. As a
benefit, this change allows rtpengine to utilize the full UDP port space
per interface address, instead of just one port space per machine.

The socket abstraction also makes it possible to support RTP over TCP in
the future.

Change-Id: If6cf4f42136229490186d2d2482fb4fc140c2b53

*  0 will allow 0 sessions (e.g. can be used for draining rtpengine)
* -1 will disable the feature and will be treated the same way as if
MAX_SESSIONS variable has not been set via configuration file
(or has been set to -1 in configuration file)
* < -1 will not be taken into consideration
* add check for minint range also

This enables switching over the endpoint of a dialogue to a new client
with potentially different capabilities

Change-Id: I973b3c5d004014cc73e6ebc3e87d03c742bc1951
(cherry picked from commit 69b7586aa4)
(cherry picked from commit 93332f0f6e)

Able to specify now, in the config, the redis databases from which rtpengine
should read and write session information.

fixes #118

additionally fixes #118

use via-branches to predict different destinations for branched SDP
offers without knowing the respective to-tag ahead of time.

Squashed commit of the following:

commit 0e81dc9828
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Thu May 21 11:06:15 2015 -0400

    fix segfault due to missing reverse tagging

commit cd7a26314b
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Thu May 21 08:57:42 2015 -0400

    support branched offer with previously unseen to-tag

commit 77da616dd2
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Wed Apr 29 11:15:37 2015 -0400

    implement via-branch handling

related to RTPENGINE-20

Squashed commit of the following:

commit 00213e66c7
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Fri Feb 27 09:40:04 2015 -0500

    perform ICE restart if we change ports

commit 27fbcbd6cb
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Thu Feb 26 15:58:12 2015 -0500

    locking fixes

commit 60c1c5ae13
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Thu Feb 26 15:58:06 2015 -0500

    unkernelize when ICE completes

commit 1d816f9864
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Thu Feb 26 15:54:44 2015 -0500

    relaxed locking where not needed

commit 75b58a9093
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Thu Feb 26 11:46:08 2015 -0500

    use atomic bitfield instead of bitfield+mutex

commit 03552eeed9
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Thu Feb 26 11:24:59 2015 -0500

    shuffle around aux.h a bit more

commit b9b8a3aa5e
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Thu Feb 26 11:16:12 2015 -0500

    remove some code redundancy through a "state machine"

commit 0b4bfef1b1
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Thu Feb 26 10:10:41 2015 -0500

    reorder to match struct

commit a2a51d81a8
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Thu Feb 26 10:10:03 2015 -0500

    clear more states for ICE restart

commit d554a2b858
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Thu Feb 26 09:58:29 2015 -0500

    dont duplicate candidates on re-invite

commit 4c804652b7
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Thu Feb 26 09:58:20 2015 -0500

    retain ICE role across re-invites

commit 4a586dd72d
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Thu Feb 26 09:42:09 2015 -0500

    eliminate duplicate log messages

commit ef0be2e308
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Thu Feb 26 09:32:36 2015 -0500

    fix incorrect log message

commit 2544b60f00
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Wed Feb 25 15:26:48 2015 -0500

    better logging for ICE agents

commit c42807384e
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Wed Feb 25 15:18:27 2015 -0500

    dont run ICE checks if we dont have a password

commit 1b56cb75b5
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Wed Feb 25 15:16:19 2015 -0500

    ICE pairs should go in triggered queue only once

commit d10c56f3ae
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Wed Feb 25 14:04:00 2015 -0500

    obsolete the ICE agent running flag

commit 52237e3399
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Wed Feb 25 14:02:06 2015 -0500

    cease checks once ICE is completed

commit 5332d18612
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Wed Feb 25 13:53:57 2015 -0500

    fix ICE completion logging

commit 85f5fd63aa
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Wed Feb 25 13:53:33 2015 -0500

    make better use of bit flags

commit 796b48bb78
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Wed Feb 25 12:09:46 2015 -0500

    improved learned candidate pairing and completion logic

commit d15561072e
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Wed Feb 25 11:21:45 2015 -0500

    support upper case transport strings

commit 557da7b1c3
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Wed Feb 25 10:43:57 2015 -0500

    use struct endpoint in ice candidates

commit 951040bfd6
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Wed Feb 25 10:31:13 2015 -0500

    more meaningful ICE log messages

commit 8ec2426bd3
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Wed Feb 25 09:54:49 2015 -0500

    shut down agent if no components - limit number of candidates

commit 149260f3a6
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Wed Feb 25 09:44:13 2015 -0500

    handle ICE restarts

commit 6a18c31f81
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Tue Feb 24 16:29:01 2015 -0500

    dont clear succeeded flag when nominating

commit 93e0861d02
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Tue Feb 24 16:21:40 2015 -0500

    use correct pwd in stun binding response

commit 32ba3ea406
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Tue Feb 24 16:03:09 2015 -0500

    use deterministic foundation for prflx cands

commit 2f2dc91515
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Tue Feb 24 15:21:13 2015 -0500

    handle initial ICE role

commit a6b8ad25e6
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Tue Feb 24 14:43:47 2015 -0500

    another ICE scheduling fix

commit c572b04e55
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Tue Feb 24 14:14:29 2015 -0500

    make ICE aware of rtcp-mux

commit 93cd2d2560
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Tue Feb 24 14:13:27 2015 -0500

    print timestamp when logging to stderr

commit 22a52ffda2
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Tue Feb 24 14:13:13 2015 -0500

    ICE scheduling fixes

commit 5d2d1a7739
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Tue Feb 24 13:27:59 2015 -0500

    increase ICE pwd length to make chrome happy

commit ceff6698db
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Tue Feb 24 13:09:54 2015 -0500

    dont discard RTP if ICE hasnt finished yet

commit e809877d0e
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Tue Feb 24 13:06:31 2015 -0500

    implement remote-candidates (untested)

commit 41670eadbb
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Tue Feb 24 11:58:13 2015 -0500

    shut down ICE agent when everything fails

commit 1ca26c4a81
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Tue Feb 24 11:10:46 2015 -0500

    fix up SDP output for ICE candidates

commit 0287d68f33
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Tue Feb 24 10:09:49 2015 -0500

    process ICE completion and fire up DTLS if desired

commit 5b6386036b
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Tue Feb 24 09:37:52 2015 -0500

    use a btree to schedule ice checks

commit 2bc25f1e0f
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Tue Feb 24 09:37:02 2015 -0500

    convert shutdown condition into global var

commit ecf0c5587c
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Mon Feb 23 14:50:46 2015 -0500

    replace poller_now with timeval g_now

commit 164ecdd7ac
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Mon Feb 23 13:00:15 2015 -0500

    handle nominations if we're controlling

commit d013659365
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Mon Feb 23 12:11:40 2015 -0500

    copy controlling/ed role into agent

commit 09f1cae14a
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Mon Feb 23 12:02:54 2015 -0500

    separate nominated pairs from valid pairs

commit f75f338cde
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Mon Feb 23 11:55:30 2015 -0500

    organize aux.h into sections

commit d6acee1392
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Mon Feb 23 11:55:17 2015 -0500

    use b-tree for various ICE lists

commit af9804d139
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Fri Feb 20 16:21:09 2015 -0500

    prepare to finalize ice processing

commit 18df118375
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Fri Feb 20 16:19:50 2015 -0500

    prettier logging

commit 280755c61a
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Fri Feb 20 15:02:14 2015 -0500

    implement unfreezing of other components on success

commit 5d13657d5b
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Fri Feb 20 15:00:24 2015 -0500

    bitfield access macros

commit 71746ad6a1
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Fri Feb 20 14:15:05 2015 -0500

    handle ice updates and duplicate candidates

commit 02309d1b5b
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Fri Feb 20 12:22:29 2015 -0500

    handle role conflicts

commit 52acf54ba5
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Fri Feb 20 10:24:01 2015 -0500

    proper pair priorities calculation

commit 307af79e8d
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Fri Feb 20 09:54:18 2015 -0500

    fix address family mixups

commit 7cbfd4d36a
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Fri Feb 20 09:14:49 2015 -0500

    delay dtls startup and timeout checks while ice is running

commit 2a8ab75228
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Thu Feb 19 16:47:56 2015 -0500

    process ice/stun responses

commit 92da323dcf
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Thu Feb 19 15:14:30 2015 -0500

    adding stun server script for testing

commit c5cfeb122c
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Thu Feb 19 13:42:40 2015 -0500

    act on stun requests, learn prflx candidates

commit 1cafd35e7a
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Thu Feb 19 13:30:14 2015 -0500

    fix pktinfo for ipv4 packets

commit 8e338b8426
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Thu Feb 19 11:48:55 2015 -0500

    rework interface handling to prepare to learn ICE candidate

commit 09e365c142
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Wed Feb 18 16:24:42 2015 -0500

    add some locking

commit 8fc7b75095
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Wed Feb 18 16:05:20 2015 -0500

    extend logic in response to stun req and implement triggered checks

commit 35eeb04376
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Wed Feb 18 12:46:42 2015 -0500

    handle ice/stun retransmits and timeouts

commit b5637565b6
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Wed Feb 18 11:19:19 2015 -0500

    first implementation of sending ICE checks

commit f0c1928c05
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Tue Feb 17 14:39:11 2015 -0500

    preliminary list and loop for ICE checks

commit c38d6e22c1
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Tue Feb 17 12:00:24 2015 -0500

    pair up candidates and prepare to run checks

commit d9559b4c59
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Fri Feb 13 15:36:29 2015 -0500

    parse and remeber basic ICE attributes

Squashed commit of the following:

commit cca40e8e31
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Thu Feb 12 10:17:51 2015 -0500

    support per-payload-type stats in kernel module

commit dcc0dc0002
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Wed Feb 11 12:14:44 2015 -0500

    count unknown rtp type as error

commit 941bde0df5
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Wed Feb 11 12:01:55 2015 -0500

    use the list of rtp formats from the m= line

    This avoids dynamically altering the rtpstats hash table and makes
    keeping packet stats lock free.

commit 9150fed671
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Fri Feb 6 15:06:04 2015 -0500

    fix and simplify rtpmap hash table

commit 1f73741cbf
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Fri Feb 6 13:56:07 2015 -0500

    MT#9935 understand, learn, remember and report RTP payload types (codecs)

commit b0d690837c
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Thu Nov 20 13:36:25 2014 -0500

    parse a=rtpmap attribute

Dieser patch beinhaltet die Anpassungen für das NG protocol.

Author:    Frederic-Philippe Metz <Frederic.Metz@1und1.de>

Die from/to information wird irgendwann generell in den tag geschrieben.
die info, ob der tag ein from_tag oder to_tag ist, wurde hinzugefügt.

Author:    Frederic-Philippe Metz <Frederic.Metz@1und1.de>

Hinzufügen der Adresse des SIP-Proxy, der die session erstellt hat
(sowohl für command line interface als auch CDR) Nur UDP control
zunächst.

Author:    Frederic-Philippe Metz <Frederic.Metz@1und1.de>

Im Telco Umfeld ist hier millisekunden-Auflösung gefordert. Nur UDP
control zunächst.

Author:    Frederic-Philippe Metz <Frederic.Metz@1und1.de>

adds CLI option --sip-source to restore old default, and adds
new flag "SIP source address" to achieve the same on a per-call
basis

fixes #44

also shuffle around some header definitions

monologue_offer_answer() had A-side and B-side reversed, resulting in
incomplete dialogue association when more than 2 parties are involved.

It also fixes #21 by catching errors returned by
monologue_offer_answer() (e.g. when running out of ports)

closes #16

* duplicate strings when filling the bencode structure
  * limit the number of results to avoid going over the UDP packet
    size limit

Fixes #3

Pending documentation