Modify D2D comms to make use of carrier configs.

- ImsPhoneCallTracker now selectively performs SDP negotiation based on
the availability of RTP / SDP for the carrier.
- RtpTransport will count itself negotiated if SDP is not in use (we will
change that in the future to do a probe/response, but for now in testing
it is sufficient).

Test: Added unit tests for carrier config cases.
Bug: 163085177
Change-Id: I6bffea3e83961afe07523a6276470ace75a7c908