Direct Media calls within private network sometimes get one way audio

When endpoints with direct_media enabled, behind a firewall (Asterisk on a
separate network) and were bridged sometimes Asterisk would send the ip
address of the firewall in the sdp to one of the phones in the reinvite
resulting in one way audio. When sending the reinvite Asterisk will retrieve
the media address from the associated rtp instance, but if frames were being
read this can be overwritten with another address (in this case the
firewall's).  This patch ensures that Asterisk uses the original device
address when using direct media.

ASTERISK-24563
Reported by: Steve Pitts
Review: https://reviewboard.asterisk.org/r/4216/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/12@429195 f38db490-d61c-443f-a65b-d21fe96a405b