AC_Fence: reset fences breach on disable

Also rename enable function parameter

libraries/AC_Fence/AC_Fence.cpp

@@ -97,6 +97,14 @@ AC_Fence::AC_Fence(const AP_AHRS& ahrs, const AP_InertialNav& inav) :
     }
 }
 
+void AC_Fence::enable(bool value)
+{
+    _enabled = value;
+    if (!value) {
+        clear_breach(AC_FENCE_TYPE_ALT_MAX | AC_FENCE_TYPE_CIRCLE | AC_FENCE_TYPE_POLYGON);
+    }
+}
+
 /// get_enabled_fences - returns bitmask of enabled fences
 uint8_t AC_Fence::get_enabled_fences() const
 {

libraries/AC_Fence/AC_Fence.h

@@ -40,7 +40,7 @@ public:
     AC_Fence(const AP_AHRS& ahrs, const AP_InertialNav& inav);
 
     /// enable - allows fence to be enabled/disabled.  Note: this does not update the eeprom saved value
-    void enable(bool true_false) { _enabled = true_false; }
+    void enable(bool value);
 
     /// enabled - returns true if fence is enabled
     bool enabled() const { return _enabled; }