EKF: ImuDownSampler pass imuSample as const reference

- inline ImuDownSampler::getDownSampledImuAndTriggerReset()
 - minor formatting and initialization cleanup

EKF/imu_down_sampler.hpp

@@ -46,18 +46,22 @@ using namespace estimator;
 
 class ImuDownSampler {
 public:
-	ImuDownSampler(float target_dt_sec);
-	~ImuDownSampler();
+	explicit ImuDownSampler(float target_dt_sec);
+	~ImuDownSampler() = default;
 
-	bool update(imuSample imu_sample_new);
-	imuSample getDownSampledImuAndTriggerReset();
+	bool update(const imuSample &imu_sample_new);
+
+	imuSample getDownSampledImuAndTriggerReset() {
+		_do_reset = true;
+		return _imu_down_sampled;
+	}
 
 private:
-	imuSample _imu_down_sampled;
-	Quatf _delta_angle_accumulated;
-	const float _target_dt;  // [sec]
-	float _imu_collection_time_adj;
-	bool _do_reset;
-
 	void reset();
+
+	imuSample _imu_down_sampled{};
+	Quatf _delta_angle_accumulated{};
+	const float _target_dt;  // [sec]
+	float _imu_collection_time_adj{0.f};
+	bool _do_reset{true};
 };