Revert "(legacy) remove global, cleanup for https://github.com/opnsense/core/issues/451"

This reverts commit 8ee0c0a2.

src/etc/inc/filter.inc

@@ -868,7 +868,7 @@ function filter_get_direct_networks_list($returnsubnetsonly = true) {
 
 function filter_generate_optcfg_array()
 {
-    global $config;
+    global $config, $FilterIflist;
 
     $FilterIflist = array();