Fix a bug where using an outbound proxy would cause the local address to be 127.0.0.1.

Copy the outbound proxy IP address into the SIP dialog structure as the IP address we will
be sending to. This has to be done because the logic that determines what local IP address to use
in the SIP messages is not aware of an outbound proxy being in place. It only knows what IP address
we are sending to.

(closes issue #12006)
Reported by: mnicholson


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@188067 65c4cc65-6c06-0410-ace0-fbb531ad65f3