ArduPlane: added RC option for new takeoff mode

ArduPlane/RC_Channel.cpp

@@ -114,6 +114,11 @@ void RC_Channel_Plane::do_aux_function(const aux_func_t ch_option, const aux_swi
         do_aux_function_change_mode(Mode::Number::RTL, ch_flag);
         break;
 
+    case AUX_FUNC::TAKEOFF:
+        do_aux_function_change_mode(Mode::Number::TAKEOFF, ch_flag);
+        break;
+
+
     default:
         RC_Channel::do_aux_function(ch_option, ch_flag);
         break;