res_pjsip_sdp_rtp: Allow only single ssrc attribute.

When processing SSRC attributes we were iterating through
all of them, even though we only need to know the remote
SSRC once. This was problematic because some browsers group
SSRCs together on a stream, and due to our negotiation only
end up using the first one. Since we set the second one as
the remote SSRC we would drop the received media from them
instead of allowing it through.

In the future this may be extended to allow SSRC groups
and to use information from the attributes.

Change-Id: I4dc87087dbe56a83aa65f0f897bbd4ca75ec1270

res/res_pjsip_sdp_rtp.c

@@ -1127,6 +1127,7 @@ static void process_ssrc_attributes(struct ast_sip_session *session, struct ast_
 		}
 
 		ast_rtp_instance_set_remote_ssrc(session_media->rtp, ssrc);
+		break;
 	}
 }