Commander: move static overload_start to class

src/modules/commander/Commander.hpp

@@ -366,6 +366,7 @@ private:
 	hrt_abstime	_boot_timestamp{0};
 	hrt_abstime	_last_disarmed_timestamp{0};
 	hrt_abstime	_timestamp_engine_healthy{0}; ///< absolute time when engine was healty
+	hrt_abstime	_overload_start{0};		///< time when CPU overload started
 
 	uint32_t	_counter{0};
 	uint8_t		_heading_reset_counter{0};