core: set response functions list after mod init

- some modules set the response function in mod_init
- case of nathelper(k)
- reported by Andres Moya

sr_module.c

@@ -899,6 +899,10 @@ int init_modules(void)
 	struct sr_module* t;
 	int i;
 	
+	i = init_mod(modules);
+	if(i!=0)
+		return i;
+
 	for(t = modules; t; t = t->next)
 		if (t->exports){
 			switch(t->mod_interface_ver){
@@ -938,7 +942,7 @@ int init_modules(void)
 		}
 	}
 	
-	return init_mod(modules);
+	return 0;
 }
 
 #endif