Plane: fixed stick mixing and throttle nudge in QRTL approach

thanks to Henry for noticing this

ArduPlane/Attitude.cpp

@@ -258,7 +258,6 @@ void Plane::stabilize_stick_mixing_fbw()
         control_mode == &mode_qhover ||
         control_mode == &mode_qloiter ||
         control_mode == &mode_qland ||
-        control_mode == &mode_qrtl ||
         control_mode == &mode_qacro ||
 #if QAUTOTUNE_ENABLED
         control_mode == &mode_qautotune ||

ArduPlane/mode.h

@@ -592,6 +592,8 @@ public:
 
     bool update_target_altitude() override;
 
+    bool allows_throttle_nudging() const override;
+
 protected:
 
     bool _enter() override;

ArduPlane/mode_qrtl.cpp

@@ -49,6 +49,12 @@ void ModeQRTL::run()
         // start landing logic
         quadplane.verify_vtol_land();
     }
+
+    // when in approach allow stick mixing
+    if (quadplane.poscontrol.get_state() == QuadPlane::QPOS_AIRBRAKE ||
+        quadplane.poscontrol.get_state() == QuadPlane::QPOS_APPROACH) {
+        plane.stabilize_stick_mixing_fbw();
+    }
 }
 
 /*
@@ -83,4 +89,10 @@ bool ModeQRTL::update_target_altitude()
     return true;
 }
 
+// only nudge during approach
+bool ModeQRTL::allows_throttle_nudging() const
+{
+    return plane.quadplane.poscontrol.get_state() == QuadPlane::QPOS_APPROACH;
+}
+
 #endif