Add support for specifying the IP address to use for media streams in sip.conf

This is the second commit for this and documents the text stream using the configured
IP address and fixes a bug in the original patch where the UDPTL stream would also
use the different IP address.

(closes issue #14729)
Reported by: _brent_
Patches:
      media_address.patch uploaded by brent (license 388)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@225089 65c4cc65-6c06-0410-ace0-fbb531ad65f3