AP_NavEKF3: Fix bug preventing copter wind estimation at low speed

Also re-tunes process noise default for smoother wind velocity state estimates.

libraries/AP_NavEKF3/AP_NavEKF3.cpp

@@ -39,7 +39,7 @@
 #define FLOW_I_GATE_DEFAULT     300
 #define CHECK_SCALER_DEFAULT    100
 #define FLOW_USE_DEFAULT        1
-#define WIND_P_NSE_DEFAULT      1.0
+#define WIND_P_NSE_DEFAULT      0.5
 
 #elif APM_BUILD_TYPE(APM_BUILD_Rover)
 // rover defaults

libraries/AP_NavEKF3/AP_NavEKF3_Control.cpp

@@ -66,7 +66,7 @@ void NavEKF3_core::setWindMagStateLearningMode()
         inhibitWindStates = true;
         updateStateIndexLim();
     } else if (inhibitWindStates && canEstimateWind &&
-               sq(stateStruct.velocity.x) + sq(stateStruct.velocity.y) > sq(5.0f)) {
+               (sq(stateStruct.velocity.x) + sq(stateStruct.velocity.y) > sq(5.0f) || dragFusionEnabled)) {
         inhibitWindStates = false;
         updateStateIndexLim();
         // set states and variances