update IMU_GYRO_DNF_BW default 8->15 Hz

- dshot telemetry feedback can be quite slow (~2 Hz), so I think a
larger default value here makes sense

src/modules/sensors/vehicle_angular_velocity/imu_gyro_parameters.c

@@ -146,4 +146,4 @@ PARAM_DEFINE_INT32(IMU_GYRO_DNF_EN, 0);
 * @min 5
 * @max 30
 */
-PARAM_DEFINE_FLOAT(IMU_GYRO_DNF_BW, 8.f);
+PARAM_DEFINE_FLOAT(IMU_GYRO_DNF_BW, 15.f);