EKF: Add multi-rotor drag model for wind estimation

EKF/optflow_fusion.cpp

@@ -510,6 +510,17 @@ void Ekf::get_flow_innov_var(float flow_innov_var[2])
 	memcpy(flow_innov_var, _flow_innov_var, sizeof(_flow_innov_var));
 }
 
+void Ekf::get_drag_innov(float drag_innov[2])
+{
+	memcpy(drag_innov, _drag_innov, sizeof(_drag_innov));
+}
+
+
+void Ekf::get_drag_innov_var(float drag_innov_var[2])
+{
+	memcpy(drag_innov_var, _drag_innov_var, sizeof(_drag_innov_var));
+}
+
 // calculate optical flow gyro bias errors
 void Ekf::calcOptFlowBias()
 {