AP_Airspeed: add rc channel option to disable all airspeed sensors

libraries/AP_Airspeed/AP_Airspeed.cpp

@@ -623,6 +623,9 @@ void AP_Airspeed::Log_Airspeed()
 
 bool AP_Airspeed::use(uint8_t i) const
 {
+    if (_force_disable_use) {
+        return false;
+    }
     if (!enabled(i) || !param[i].use) {
         return false;
     }

libraries/AP_Airspeed/AP_Airspeed.h

@@ -96,6 +96,11 @@ public:
     bool use(uint8_t i) const;
     bool use(void) const { return use(primary); }
 
+    // force disabling of all airspeed sensors
+    void force_disable_use(bool value) {
+        _force_disable_use = value;
+    }
+
     // return true if airspeed is enabled
     bool enabled(uint8_t i) const {
         if (i < AIRSPEED_MAX_SENSORS) {
@@ -236,6 +241,9 @@ private:
 
     bool calibration_enabled;
 
+    // can be set to true to disable the use of the airspeed sensor
+    bool _force_disable_use;
+
     // current primary sensor
     uint8_t primary;
     uint8_t num_sensors;