Rover: support do-mount-control via command-long

APMrover2/GCS_Mavlink.cpp

@@ -920,6 +920,12 @@ void GCS_MAVLINK::handleMessage(mavlink_message_t* msg)
                 break;
 #endif
 
+            case MAV_CMD_DO_MOUNT_CONTROL:
+#if MOUNT == ENABLED
+                rover.camera_mount.control(packet.param1, packet.param2, packet.param3, (MAV_MOUNT_MODE) packet.param7);
+#endif
+                break;
+
             case MAV_CMD_MISSION_START:
                 rover.set_mode(AUTO);
                 result = MAV_RESULT_ACCEPTED;