Latency measurements: Estimate latency based on sensor timestamp through full system

src/modules/fw_att_control/fw_att_control_main.cpp

@@ -1060,7 +1060,9 @@ FixedwingAttitudeControl::task_main()
 
 			/* lazily publish the setpoint only once available */
 			_actuators.timestamp = hrt_absolute_time();
+			_actuators.timestamp_sample = _att.timestamp;
 			_actuators_airframe.timestamp = hrt_absolute_time();
+			_actuators_airframe.timestamp_sample = _att.timestamp;
 
 			/* publish the actuator controls */
 			if (_actuators_0_pub > 0) {

src/modules/uORB/topics/actuator_controls.h

@@ -62,6 +62,7 @@
 
 struct actuator_controls_s {
 	uint64_t timestamp;
+	uint64_t timestamp_sample;			/**< the timestamp the data this control response is based on was sampled */
 	float	control[NUM_ACTUATOR_CONTROLS];
 };