EKF: Don't run unnecessary makeRowColSymmetric operation

This operation is expensive when done to the whole covariance matrix and unnecessary after covariance prediction because we calculate the upper diagonal and copy across so it is already symmetric.

EKF/optflow_fusion.cpp

@@ -501,7 +501,7 @@ void Ekf::fuseOptFlow()
 			}
 
 			// correct the covariance matrix for gross errors
-			fixCovarianceErrors();
+			fixCovarianceErrors(true);
 
 			// apply the state corrections
 			fuse(gain, _flow_innov[obs_index]);