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

APMrover2/GCS_Mavlink.cpp

@@ -58,7 +58,7 @@ uint32_t GCS_Rover::custom_mode() const
     return rover.control_mode->mode_number();
 }
 
-MAV_STATE GCS_MAVLINK_Rover::system_status() const
+MAV_STATE GCS_MAVLINK_Rover::vehicle_system_status() const
 {
     if ((rover.failsafe.triggered != 0) || rover.failsafe.ekf) {
         return MAV_STATE_CRITICAL;

APMrover2/GCS_Mavlink.h

@@ -43,7 +43,7 @@ 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;
 
     int16_t vfr_hud_throttle() const override;