AP_NavEKF3: pass by const reference when needed

libraries/AP_NavEKF3/AP_NavEKF3_core.cpp

@@ -1393,7 +1393,7 @@ void NavEKF3_core::StoreQuatReset()
 }
 
 // Rotate the stored output quaternion history through a quaternion rotation
-void NavEKF3_core::StoreQuatRotate(Quaternion deltaQuat)
+void NavEKF3_core::StoreQuatRotate(const Quaternion &deltaQuat)
 {
     outputDataNew.quat = outputDataNew.quat*deltaQuat;
     // write current measurement to entire table
@@ -1665,7 +1665,7 @@ Vector3f NavEKF3_core::calcRotVecVariances()
 }
 
 // initialise the quaternion covariances using rotation vector variances
-void NavEKF3_core::initialiseQuatCovariances(Vector3f &rotVarVec)
+void NavEKF3_core::initialiseQuatCovariances(const Vector3f &rotVarVec)
 {
     // calculate an equivalent rotation vector from the quaternion
     float q0 = stateStruct.quat[0];

libraries/AP_NavEKF3/AP_NavEKF3_core.h

@@ -561,7 +561,7 @@ private:
     void StoreQuatReset(void);
 
     // Rotate the stored output quaternion history through a quaternion rotation
-    void StoreQuatRotate(Quaternion deltaQuat);
+    void StoreQuatRotate(const Quaternion &deltaQuat);
 
     // store altimeter data
     void StoreBaro();
@@ -790,7 +790,7 @@ private:
     Vector3f calcRotVecVariances(void);
     
     // initialise the quaternion covariances using rotation vector variances
-    void initialiseQuatCovariances(Vector3f &rotVarVec);
+    void initialiseQuatCovariances(const Vector3f &rotVarVec);
 
     // update timing statistics structure
     void updateTimingStatistics(void);