Revert "leave out rtcp attribute in rtcp-mux case"

This reverts commit c7477e3fa9.

daemon/sdp.c

@@ -1500,7 +1500,9 @@ int sdp_replace(struct sdp_chopper *chop, GQueue *sessions, struct call *call,
 				chopper_append_c(chop, "\r\n");
 			}
 			else if (r_flags == 2) {
-				chopper_append_c(chop, "a=rtcp-mux\r\n");
+				chopper_append_c(chop, "a=rtcp:");
+				chopper_append_printf(chop, "%hu", rtp->fd.localport);
+				chopper_append_c(chop, "\r\na=rtcp-mux\r\n");
 			}
 
 			generate_crypto(media, flags, rtp, rtcp, chop);