Plane: fixed startup order of setting mavlink system ID

ArduPlane/system.cpp

@@ -118,6 +118,8 @@ void Plane::init_ardupilot()
 
     GCS_MAVLINK::set_dataflash(&DataFlash);
 
+    mavlink_system.sysid = g.sysid_this_mav;
+
     // initialise serial ports
     serial_manager.init();
     gcs[0].setup_uart(serial_manager, AP_SerialManager::SerialProtocol_MAVLink, 0);
@@ -165,8 +167,6 @@ void Plane::init_ardupilot()
                          &g.fs_batt_voltage, &g.fs_batt_mah);
 #endif
 
-    mavlink_system.sysid = g.sysid_this_mav;
-
 #if LOGGING_ENABLED == ENABLED
     log_init();
 #endif