rc: need $fp for manual DNS server

src/etc/rc.initial.setlanip

@@ -206,7 +206,7 @@ function next_unused_gateway_name($interface)
 
 function add_gateway_to_config($interface, $gatewayip, $inet_type, $is_in_subnet)
 {
-    global $config;
+    global $config, $fp;
 
     $label_IPvX = $inet_type == 'inet6' ? 'IPv6' : 'IPv4';