mavlink: use optical flow limits from params

This makes more sense than hard-coding arbitrary values.

src/modules/mavlink/mavlink_receiver.cpp

@@ -829,8 +829,8 @@ MavlinkReceiver::handle_message_optical_flow_rad(mavlink_message_t *msg)
 		device_id.devid_s.address = msg->sysid;
 
 		d.timestamp = f.timestamp;
-		d.min_distance = 0.3f;
-		d.max_distance = 5.0f;
+		d.min_distance = _param_ekf2_min_rng.get();
+		d.max_distance = _param_ekf2_rng_a_hmax.get();
 		d.current_distance = flow.distance; /* both are in m */
 		d.type = distance_sensor_s::MAV_DISTANCE_SENSOR_ULTRASOUND;
 		d.device_id = device_id.devid;

src/modules/mavlink/mavlink_receiver.h

@@ -403,7 +403,9 @@ private:
 	DEFINE_PARAMETERS(
 		(ParamFloat<px4::params::BAT_CRIT_THR>)     _param_bat_crit_thr,
 		(ParamFloat<px4::params::BAT_EMERGEN_THR>)  _param_bat_emergen_thr,
-		(ParamFloat<px4::params::BAT_LOW_THR>)      _param_bat_low_thr
+		(ParamFloat<px4::params::BAT_LOW_THR>)      _param_bat_low_thr,
+		(ParamFloat<px4::params::EKF2_MIN_RNG>)     _param_ekf2_min_rng,
+		(ParamFloat<px4::params::EKF2_RNG_A_HMAX>)  _param_ekf2_rng_a_hmax
 	);
 
 	// Disallow copy construction and move assignment.