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

ArduCopter/GCS_Mavlink.cpp

@@ -72,7 +72,7 @@ uint32_t GCS_Copter::custom_mode() const
     return (uint32_t)copter.control_mode;
 }
 
-MAV_STATE GCS_MAVLINK_Copter::system_status() const
+MAV_STATE GCS_MAVLINK_Copter::vehicle_system_status() const
 {
     // set system as critical if any failsafe have triggered
     if (copter.any_failsafe_triggered())  {

ArduCopter/GCS_Mavlink.h

@@ -57,7 +57,7 @@ private:
                         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;
 
     int16_t vfr_hud_throttle() const override;
     float vfr_hud_alt() const override;