Changes

asterisk: pjsip.conf: identify incoming register started by local SIP UAs

This config section is needed so that Asterisk can figure out the endpoint
when receiving a "REGISTER sip:172.18.248.10". Without it, it will answer with
a 404 Not Found.

Change-Id: I39568c3cebb89fc5a62a8144f448b50c48d79f10