res_pjsip_session: initialize pending's topology to endpoint's

Found during some testing, there is a race condition between selecting an
appropriate bridge type for a call versus the applying of media on the callee's
session. In some instances a native bridge type would have been chosen, but
due to the callee's media not yet being established at bridge compatibility
check time the simple bridge type is picked instead.

When using chan_pjsip this initiates a topology change event. The topologies
are then compared for the two sessions. However, when the topology was created
for the caller its streams are initialized to "inactive". This topology is then
used as a base when creating the callee's topology, and streams. Soon after
the caller's topology's stream(s) get updated based on the sdp (get set to
sendrecv in the failing scenario).

Now when the topology change event is raised, and the two topologies are
compared, the comparison fails due to a stream state mismatch (sendrecv vs
inactive). And since they differ a reinvite is sent out (to the caller in
this case).

This patch makes it such that when the caller's topology is initially created
it gets created based on its configured endpoint's media topology. When the
endpoint's topology is created its stream's state(s) are initialized to
sendrecv instead of inactive. Subsequently, now when the callee's topology is
created its topology streams are now initialized to sendrecv. Thus when the
topology change event occurs due to the mentioned scenario the stream states
match for the given sessions, and the reinvite is not sent unless due to some
other valid mismatch.

Note, this patch only changes one pending media state's creation point. It's
possible other places *could* be changed, however for now it was deemed best
to only alter what's here.

Change-Id: I6ba3a6a75f64824a1b963044c37acbe951c389c7

res/res_pjsip_session.c

@@ -712,7 +712,7 @@ static int handle_incoming_sdp(struct ast_sip_session *session, const pjmedia_sd
 
 	/* It is possible for SDP deferral to have already created a pending topology */
 	if (!session->pending_media_state->topology) {
-		session->pending_media_state->topology = ast_stream_topology_alloc();
+		session->pending_media_state->topology = ast_stream_topology_clone(session->endpoint->media.topology);
 		if (!session->pending_media_state->topology) {
 			return -1;
 		}