send_dummy: Use proper condition to test if conn is osmux

Change-Id: I493e7afaf8e6edb5bf975b3097fab49986d064cf
diff --git a/src/libosmo-mgcp/mgcp_protocol.c b/src/libosmo-mgcp/mgcp_protocol.c
index 79fbc53..5493917 100644
--- a/src/libosmo-mgcp/mgcp_protocol.c
+++ b/src/libosmo-mgcp/mgcp_protocol.c
@@ -323,7 +323,7 @@
  * osmux connection, send the dummy packet via OSMUX */
 static void send_dummy(struct mgcp_endpoint *endp, struct mgcp_conn_rtp *conn)
 {
-	if (conn->osmux.state != OSMUX_STATE_DISABLED)
+	if (mgcp_conn_rtp_is_osmux(conn))
 		osmux_send_dummy(endp, conn);
 	else
 		mgcp_send_dummy(endp, conn);