Small fix on config revert, loosly related to https://github.com/opnsense/core/issues/124

Use internal classes to restore a backup, to prevent overwrite by our singleton object

src/etc/inc/config.lib.inc

@@ -235,18 +235,12 @@ function config_restore($conffile) {
 
 	$cnf = OPNsense\Core\Config::getInstance();
 	$cnf->backup();
-
-	$lockkey = lock('config', LOCK_EX);
-
-	copy($conffile, '/conf/config.xml');
+	$cnf->restoreBackup($conffile);
 
 	disable_security_checks();
 
-	unlock($lockkey);
-
 	$config = parse_config();
 
-
 	write_config(gettext("Reverted to") . " " . array_pop(explode("/", $conffile)) . ".", false);
 
 	return 0;