ekf2: move estimator_sensor_bias publication to method

- only publish if there's a change in bias
 - publish current estimated mag bias, including saved mag bias

src/modules/ekf2/EKF2.hpp

@@ -138,6 +138,7 @@ private:
 	void PublishEkfDriftMetrics(const hrt_abstime &timestamp);
 	void PublishOpticalFlowVel(const hrt_abstime &timestamp, const optical_flow_s &optical_flow);
 	void PublishOdometry(const hrt_abstime &timestamp, const imuSample &imu);
+	void PublishSensorBias(const hrt_abstime &timestamp);
 	void PublishWindEstimate(const hrt_abstime &timestamp);
 	void PublishYawEstimatorStatus(const hrt_abstime &timestamp);
 
@@ -191,6 +192,10 @@ private:
 
 	Vector3f _last_local_position_for_gpos{};
 
+	Vector3f _last_accel_bias{};
+	Vector3f _last_gyro_bias{};
+	Vector3f _last_mag_bias{};
+
 	uORB::Subscription _airdata_sub{ORB_ID(vehicle_air_data)};
 	uORB::Subscription _airspeed_sub{ORB_ID(airspeed)};
 	uORB::Subscription _ev_odom_sub{ORB_ID(vehicle_visual_odometry)};