don't depend on EXT_NOTIFY_OUT being defined.

src/modules/ExternalNotificationModule.h

@@ -12,8 +12,8 @@
  */
 class ExternalNotificationModule : public SinglePortModule, private concurrency::OSThread
 {
-  uint32_t output = EXT_NOTIFY_OUT;
-  
+  uint32_t output = 0;
+
   public:
     ExternalNotificationModule();