mgw: Add first tests for testing RTP streams

The existing MGW tests were entirely on the MGCP side.  Let's start
some tests that exchange RTP frames with the MGW and validate that
the MGW can actually act on what is configured via MGCP.

Change-Id: If620d5f8927d0e3584e90a7a8f785c6fdd7c2d17
2 files changed