PJSIP: Fix address for ACK in NAT situations

PJSIP: Fix address for ACK in NAT situations

In NAT scenarios where a call is placed to a Grandstream phone,
res_pjsip will sometimes send the ACK to a 200 OK to the private
address of the device behind the NAT instead of the address of the NAT
device. This corrects that behavior by rewriting the address in the
Contact header in the incoming 200 OK and the dialog's target address
if necessary (since it has already been rewritten to the incorrect
private address).

(closes issue ASTERISK-23106)
Review: https://reviewboard.asterisk.org/r/3168/
Reported by: Matt Jordan

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/12@407000 65c4cc65-6c06-0410-ace0-fbb531ad65f3