filter: fix typo uncovered while testing

This brings us down from 2.2 seconds to 0.2 seconds reload time
*without* the obscure caching in place.  This will likely solve
the filter reload issues that some people had.  :)

(cherry picked from commit 2c5d626c)

src/etc/inc/filter.inc

@@ -1368,7 +1368,7 @@ function filter_generate_reflection_proxy(&$FilterIflist, $rule, $nordr, $rdr_if
     return $natrules;
 }
 
-function filter_nat_rules_automatic_tonathosts(&$filterIflist, $with_descr = false)
+function filter_nat_rules_automatic_tonathosts(&$FilterIflist, $with_descr = false)
 {
     global $config, $GatewaysList;