mavlink: fix transmitting vehicle commands

src/modules/mavlink/mavlink_main.cpp

@@ -1337,6 +1337,7 @@ void Mavlink::send_protocol_version()
 
 MavlinkOrbSubscription *Mavlink::add_orb_subscription(const orb_id_t topic, int instance)
 {
+	if (topic != ORB_ID(vehicle_command)) {
 		/* check if already subscribed to this topic */
 		MavlinkOrbSubscription *sub;
 
@@ -1346,6 +1347,7 @@ MavlinkOrbSubscription *Mavlink::add_orb_subscription(const orb_id_t topic, int
 				return sub;
 			}
 		}
+	}
 
 	/* add new subscription */
 	MavlinkOrbSubscription *sub_new = new MavlinkOrbSubscription(topic, instance);