Plane: rename system_status as it won't be called from base class

ArduPlane/GCS_Mavlink.cpp

@@ -93,7 +93,7 @@ uint32_t GCS_Plane::custom_mode() const
     return plane.control_mode->mode_number();
 }
 
-MAV_STATE GCS_MAVLINK_Plane::system_status() const
+MAV_STATE GCS_MAVLINK_Plane::vehicle_system_status() const
 {
     if (plane.control_mode == &plane.mode_initializing) {
         return MAV_STATE_CALIBRATING;

ArduPlane/GCS_Mavlink.h

@@ -55,7 +55,7 @@ private:
     void packetReceived(const mavlink_status_t &status, const mavlink_message_t &msg) override;
 
     MAV_MODE base_mode() const override;
-    MAV_STATE system_status() const override;
+    MAV_STATE vehicle_system_status() const override;
 
     uint8_t radio_in_rssi() const;