EKF: Add method to enable the IMU bias states to be reset externally

EKF/estimator_interface.h

@@ -192,6 +192,13 @@ public:
 	// set vehicle landed status data
 	void set_in_air_status(bool in_air) {_control_status.flags.in_air = in_air;}
 
+	/*
+	Reset all IMU bias states and covariances to initial alignment values.
+	Use when the IMU sensor has changed.
+	Returns true if reset performed, false if rejected due to less than 10 seconds lapsed since last reset.
+	*/
+	virtual bool reset_imu_bias() = 0;
+
 	// get vehicle landed status data
 	bool get_in_air_status() {return _control_status.flags.in_air;}