PJSIP: Force transport on contact rewrite

PJSIP: Force transport on contact rewrite

If contact rewriting is enabled but the contact differs in transport
from what is actually being used, messages after the initial INVITE
transaction can be sent to an incorrect transport/port combination. In
the case where this bug occurred the remote party never received a BYE
since it was sent to the remote party's TCP port over UDP.

Review: https://reviewboard.asterisk.org/r/4032/

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/12@424244 65c4cc65-6c06-0410-ace0-fbb531ad65f3