blocking-queue: Fix incompatible function types warning

src/libstrongswan/collections/blocking_queue.c

@@ -97,10 +97,19 @@ METHOD(blocking_queue_t, destroy_offset, void,
 	destroy(this);
 }
 
+CALLBACK(destroy_item, void,
+	void *item, va_list args)
+{
+	void (*fn)(void*);
+
+	VA_ARGS_VGET(args, fn);
+	fn(item);
+}
+
 METHOD(blocking_queue_t, destroy_function, void,
 	private_blocking_queue_t *this, void (*fn)(void*))
 {
-	this->list->invoke_function(this->list, (linked_list_invoke_t)fn);
+	this->list->invoke_function(this->list, destroy_item, fn);
 	destroy(this);
 }