MGW_Tests: Add test for "confecho" connection.

The test uses two connections: "confecho" and "sendonly". It is expected
that "confecho" connection receives as many RTP packets as it sends,
because it echoes back its packets. It is also expected that "sendonly"
connection receives the same amount of RTP packets.

Change-Id: I7df4a58ad9287a564b2daf7548b882c03787f7f2
1 file changed