Plane: fixed a bug where mode would not revert on geo-fence disable

the mode would not revert if the switch was in position 0

ArduPlane/ArduPlane.pde

@@ -350,12 +350,14 @@ static bool usb_connected;
 ////////////////////////////////////////////////////////////////////////////////
 // This is the state of the flight control system
 // There are multiple states defined such as MANUAL, FBW-A, AUTO
-enum FlightMode control_mode  = INITIALISING;
+static enum FlightMode control_mode  = INITIALISING;
+
 // Used to maintain the state of the previous control switch position
-// This is set to -1 when we need to re-read the switch
-uint8_t oldSwitchPosition;
+// This is set to 254 when we need to re-read the switch
+static uint8_t oldSwitchPosition = 254;
+
 // This is used to enable the inverted flight feature
-bool inverted_flight     = false;
+static bool inverted_flight     = false;
 
 static struct {
     // These are trim values used for elevon control

ArduPlane/control_modes.pde

@@ -70,7 +70,7 @@ static uint8_t readSwitch(void){
 
 static void reset_control_switch()
 {
-    oldSwitchPosition = 0;
+    oldSwitchPosition = 254;
     read_control_switch();
 }
 

ArduPlane/geofence.pde

@@ -87,6 +87,7 @@ static void geofence_load(void)
             // not much we can do here except disable it
             goto failed;
         }
+        geofence_state->old_switch_position = 254;
     }
 
     if (g.fence_total <= 0) {
@@ -188,7 +189,7 @@ static void geofence_check(bool altitude_check_only)
             geofence_state->old_switch_position == oldSwitchPosition &&
             guided_WP.lat == geofence_state->boundary[0].x &&
             guided_WP.lng == geofence_state->boundary[0].y) {
-            geofence_state->old_switch_position = 0;
+            geofence_state->old_switch_position = 254;
             reset_control_switch();
         }
         return;