Plane: add arm/disarm on aux switch

ArduPlane/Plane.h

@@ -150,6 +150,7 @@ public:
     friend class AP_AdvancedFailsafe_Plane;
     friend class AP_Avoidance_Plane;
     friend class GCS_Plane;
+    friend class RC_Channel_Plane;
     friend class RC_Channels_Plane;
 
     Plane(void);

ArduPlane/RC_Channel.cpp

@@ -26,3 +26,40 @@ bool RC_Channels_Plane::has_valid_input() const
     }
     return true;
 }
+
+void RC_Channel_Plane::init_aux_function(const RC_Channel::aux_func_t ch_option,
+                                         const RC_Channel::aux_switch_pos_t ch_flag)
+{
+    switch(ch_option) {
+    // the following functions do not need to be initialised:
+    case ARMDISARM:
+        break;
+    default:
+        RC_Channel::init_aux_function(ch_option, ch_flag);
+        break;
+}
+}
+
+// do_aux_function - implement the function invoked by auxillary switches
+void RC_Channel_Plane::do_aux_function(const aux_func_t ch_option, const aux_switch_pos_t ch_flag)
+{
+    switch(ch_option) {
+    case ARMDISARM:
+        // arm or disarm the vehicle
+        switch (ch_flag) {
+        case HIGH:
+            plane.arm_motors(AP_Arming::ArmingMethod::AUXSWITCH, true);
+            break;
+        case MIDDLE:
+            // nothing
+            break;
+        case LOW:
+            plane.disarm_motors();
+            break;
+        }
+        break;
+    default:
+        RC_Channel::do_aux_function(ch_option, ch_flag);
+        break;
+    }
+}

ArduPlane/RC_Channel.h

@@ -9,6 +9,11 @@ public:
 
 protected:
 
+    void init_aux_function(aux_func_t ch_option,
+                           aux_switch_pos_t ch_flag) override;
+    void do_aux_function(aux_func_t ch_option, aux_switch_pos_t) override;
+
+
 private:
 
 };