res_pjsip_sdp_rtp: RTP instance does not use same IP as explicit transport

Currently a wildcard address is used for the local RTP socket, which
will not always result in the same address as used by the SIP socket
(e.g. if explicit transport addresses are configured).
Use the transport's host address when binding new local RTP sockets if
available.

ASTERISK-26851

Change-Id: I098c29c9d1f79a4f970d72ba894874ac75954f1a

res/res_pjsip_sdp_rtp.c

@@ -196,6 +196,20 @@ static int create_rtp(struct ast_sip_session *session, struct ast_sip_session_me
 	if (session->endpoint->media.bind_rtp_to_media_address && !ast_strlen_zero(session->endpoint->media.address)) {
 		ast_sockaddr_parse(&temp_media_address, session->endpoint->media.address, 0);
 		media_address = &temp_media_address;
+	} else {
+		struct ast_sip_transport *transport =
+			ast_sorcery_retrieve_by_id(ast_sip_get_sorcery(), "transport",
+									   session->endpoint->transport);
+
+		if (transport && transport->state) {
+			char hoststr[PJ_INET6_ADDRSTRLEN];
+
+			pj_sockaddr_print(&transport->state->host, hoststr, sizeof(hoststr), 0);
+			ast_debug(1, "Transport: %s bound to host: %s, using this for media.\n",
+					  session->endpoint->transport, hoststr);
+			ast_sockaddr_parse(media_address, hoststr, 0);
+		}
+		ao2_cleanup(transport);
 	}
 
 	if (!(session_media->rtp = ast_rtp_instance_new(session->endpoint->media.rtp.engine, sched, media_address, NULL))) {