netfilter: ctnetlink: fix filtering with CTA_TUPLE_REPLY

filter->orig_flags was used for a reply context.

Fixes: cb8aa9a3 ("netfilter: ctnetlink: add kernel side filtering for dump")
Signed-off-by: Florent Fourcot <florent.fourcot@wifirst.fr>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>