This patch forces rtpengine to use the IPv4 TTL and IPv6 hop limits set
on the host for proxied packets in kernel mode.
Beforehand, the TTL was always set to a hardcoded value of 64. While
this is the default almost everywhere, it may be desirable to be able to
set a higher value. Especially when interfacing with complex carrier
backbone networks.
Closes#1860
Change-Id: I2ddf5752db541205d92f042db22eb738481e84a3