closes #169

Change-Id: I0560aa9a4a48e39bc5d1c667362cd58c557499dd
(cherry picked from commit ed75c99a2d)

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)

closes #117

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

don't apply the regular RTP timeout to call legs which haven't been
"filled" yet, instead use the silent-timeout

fixes #105

workaround as per issue #102 for broken audio after SSRC change by
hold/unhold. workaround before full multi-SSRC support is available.

as suggested in issue #65

use presence of ufrag attribute to detect ICE support instead of
candidates

fixes double-free and mem corruption bugs (segfault fix)

closes #96

closes #92

Fixes #90

fixes #84

Fixes #80

fixes #78

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

Creates a preliminary log tag with the call-id whenever possible.

Changes log level of underlying NG messages to DEBUG.

Does a pretty-printed dump of NG responses.

Closes #73

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