AntennaTracker: added SERIAL_CONTROL support

allows for radio update and config over USB

Tools/AntennaTracker/GCS_Mavlink.pde

@@ -905,6 +905,12 @@ mission_failed:
         break;
     }
 
+#if HAL_CPU_CLASS > HAL_CPU_CLASS_16
+    case MAVLINK_MSG_ID_SERIAL_CONTROL:
+        handle_serial_control(msg, gps);
+        break;
+#endif
+
     default:
         break;