mag_cal: fix mag bias estimate to mag cal

- since last_us is set to 0 every time the bias is not observable, the
  total time was also reset -> needed 30 consecutive seconds in mag 3D
  to be declared "stable"
- after landing, the mag_aligned_in_flight flag is reset. Using this for
  bias validity makes it invalid before we have a chance to save it to
  the calibration.

src/lib/sensor_calibration/Magnetometer.cpp

@@ -110,7 +110,7 @@ void Magnetometer::SensorCorrectionsUpdate(bool force)
 
 bool Magnetometer::set_offset(const Vector3f &offset)
 {
-	if (Vector3f(_offset - offset).longerThan(0.01f)) {
+	if (Vector3f(_offset - offset).longerThan(0.005f)) {
 		if (offset.isAllFinite()) {
 			_offset = offset;
 			_calibration_count++;

src/modules/ekf2/EKF2.cpp

@@ -2456,8 +2456,10 @@ void EKF2::UpdateCalibration(const hrt_abstime &timestamp, InFlightCalibration &
 		// consider bias estimates stable when all checks pass consistently and bias hasn't changed more than 10% of the limit
 		const float bias_change_limit = 0.1f * bias_limit;
 
-		if ((cal.last_us != 0) && !(cal.bias - bias).longerThan(bias_change_limit)) {
-			cal.total_time_us += timestamp - cal.last_us;
+		if (!(cal.bias - bias).longerThan(bias_change_limit)) {
+			if (cal.last_us != 0) {
+				cal.total_time_us += timestamp - cal.last_us;
+			}
 
 			if (cal.total_time_us > 30_s) {
 				cal.cal_available = true;
@@ -2517,7 +2519,6 @@ void EKF2::UpdateGyroCalibration(const hrt_abstime &timestamp)
 void EKF2::UpdateMagCalibration(const hrt_abstime &timestamp)
 {
 	const bool bias_valid = (_ekf.control_status_flags().mag_hdg || _ekf.control_status_flags().mag_3D)
-				&& _ekf.control_status_flags().mag_aligned_in_flight
 				&& !_ekf.control_status_flags().mag_fault
 				&& !_ekf.control_status_flags().mag_field_disturbed;
 

src/modules/sensors/vehicle_magnetometer/VehicleMagnetometer.cpp

@@ -329,7 +329,7 @@ void VehicleMagnetometer::UpdateMagCalibration()
 
 					if (_calibration[mag_index].set_offset(mag_cal_offset)) {
 
-						PX4_INFO("%d (%" PRIu32 ") EST:%d offset: [%.2f, %.2f, %.2f]->[%.2f, %.2f, %.2f] (full [%.3f, %.3f, %.3f])",
+						PX4_INFO("%d (%" PRIu32 ") EST:%d offset: [%.3f, %.3f, %.3f]->[%.3f, %.3f, %.3f] (full [%.3f, %.3f, %.3f])",
 							 mag_index, _calibration[mag_index].device_id(), i,
 							 (double)mag_cal_orig(0), (double)mag_cal_orig(1), (double)mag_cal_orig(2),
 							 (double)mag_cal_offset(0), (double)mag_cal_offset(1), (double)mag_cal_offset(2),