ekf2: new gyro bias limit parameter EKF2_GYR_B_LIM

- default is now a more conservative 0.15 rad/s (~8.6 deg/s) instead of the previous hardcoded 20 deg/s

src/modules/ekf2/EKF/common.h

@@ -434,6 +434,8 @@ struct parameters {
 	float acc_bias_learn_gyr_lim{3.0f};     ///< learning is disabled if the magnitude of the IMU angular rate vector is greater than this (rad/sec)
 	float acc_bias_learn_tc{0.5f};          ///< time constant used to control the decaying envelope filters applied to the accel and gyro magnitudes (sec)
 
+	float gyro_bias_lim{0.4f};              ///< maximum gyro bias magnitude (rad/sec)
+
 	const unsigned reset_timeout_max{7'000'000};      ///< maximum time we allow horizontal inertial dead reckoning before attempting to reset the states to the measurement or change _control_status if the data is unavailable (uSec)
 	const unsigned no_aid_timeout_max{1'000'000};     ///< maximum lapsed time from last fusion of a measurement that constrains horizontal velocity drift before the EKF will determine that the sensor is no longer contributing to aiding (uSec)
 	const unsigned hgt_fusion_timeout_max{5'000'000}; ///< maximum time we allow height fusion to fail before attempting a reset or stopping the fusion aiding (uSec)

src/modules/ekf2/EKF/ekf.h

@@ -306,7 +306,7 @@ public:
 	// gyro bias (states 10, 11, 12)
 	Vector3f getGyroBias() const { return _state.delta_ang_bias / _dt_ekf_avg; } // get the gyroscope bias in rad/s
 	Vector3f getGyroBiasVariance() const { return Vector3f{P(10, 10), P(11, 11), P(12, 12)} / sq(_dt_ekf_avg); } // get the gyroscope bias variance in rad/s
-	float getGyroBiasLimit() const { return math::radians(20.f); } // 20 degrees/s
+	float getGyroBiasLimit() const { return _params.gyro_bias_lim; }
 
 	// accel bias (states 13, 14, 15)
 	Vector3f getAccelBias() const { return _state.delta_vel_bias / _dt_ekf_avg; } // get the accelerometer bias in m/s**2