ekf2: extend sensor bias stability requirement

- for accel/gyro/mag estimated bias only consider them stable (valid
for calibration updates) if the value isn't changing (10% of limit) over
the validity period

src/modules/ekf2/EKF2.hpp

@@ -171,6 +171,16 @@ private:
 	void UpdateMagSample(ekf2_timestamps_s &ekf2_timestamps);
 	void UpdateRangeSample(ekf2_timestamps_s &ekf2_timestamps);
 
+	// Used to check, save and use learned accel/gyro/mag biases
+	struct InFlightCalibration {
+		hrt_abstime last_us{0};         ///< last time the EKF was operating a mode that estimates accelerometer biases (uSec)
+		hrt_abstime total_time_us{0};   ///< accumulated calibration time since the last save
+		matrix::Vector3f bias{};
+		bool cal_available{false};      ///< true when an unsaved valid calibration for the XYZ accelerometer bias is available
+	};
+
+	void UpdateCalibration(const hrt_abstime &timestamp, InFlightCalibration &cal, const matrix::Vector3f &bias,
+			       const matrix::Vector3f &bias_variance, float bias_limit, bool bias_valid, bool learning_valid);
 	void UpdateAccelCalibration(const hrt_abstime &timestamp);
 	void UpdateGyroCalibration(const hrt_abstime &timestamp);
 	void UpdateMagCalibration(const hrt_abstime &timestamp);
@@ -225,13 +235,6 @@ private:
 	// Used to control saving of mag declination to be used on next startup
 	bool _mag_decl_saved = false;	///< true when the magnetic declination has been saved
 
-	// Used to check, save and use learned accel/gyro/mag biases
-	struct InFlightCalibration {
-		hrt_abstime last_us{0};         ///< last time the EKF was operating a mode that estimates accelerometer biases (uSec)
-		hrt_abstime total_time_us{0};   ///< accumulated calibration time since the last save
-		bool cal_available{false};      ///< true when an unsaved valid calibration for the XYZ accelerometer bias is available
-	};
-
 	InFlightCalibration _accel_cal{};
 	InFlightCalibration _gyro_cal{};
 	InFlightCalibration _mag_cal{};