Changes

asterisk: Enable IMS port advanced mode

This allows the SIPmsg_PT port module to be able to handle multiple
client sockets concurrently.
This allows workarounding for now a bug where Asterisk wrongly creates a
TCP conn 2 times and sending the REGISTER over the 2nd one, while TTCN3
operates only on the 1st accepted socket.

Change-Id: I287650a42c700c3959d0959620fb3f1e8e342c7d