don't shut down ICE agent on consecutive re-invites

fixes #103

daemon/call.c

@@ -2432,10 +2432,12 @@ static void __rtp_payload_types(struct call_media *media, GQueue *types) {
 }
 
 static void __ice_start(struct call_media *media) {
-	if (!MEDIA_ISSET(media, ICE) || MEDIA_ISSET(media, PASSTHRU)) {
+	if (MEDIA_ISSET(media, PASSTHRU)) {
 		ice_shutdown(&media->ice_agent);
 		return;
 	}
+	if (!MEDIA_ISSET(media, ICE)) /* don't init new ICE agent but leave it running if there is one */
+		return;
 
 	ice_agent_init(&media->ice_agent, media);
 }

daemon/sdp.c

@@ -2014,7 +2014,7 @@ int sdp_replace(struct sdp_chopper *chop, GQueue *sessions, struct call_monologu
 			insert_crypto(call_media, chop);
 			insert_dtls(call_media, chop);
 
-			if (call_media->ice_agent) {
+			if (MEDIA_ISSET(call_media, ICE)) {
 				chopper_append_c(chop, "a=ice-ufrag:");
 				chopper_append_str(chop, &call_media->ice_agent->ufrag[1]);
 				chopper_append_c(chop, "\r\na=ice-pwd:");