netfilter: ebt_ip6: fix source and destination matching

This bug was introduced on commit 0898f99a

. This just recovers two
checks that existed before as suggested by Bart De Schuymer.

Signed-off-by: Luís Fernando Cornachioni Estrozi <lestrozi@uolinc.com>
Signed-off-by: Bart De Schuymer <bdschuym@pandora.be>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>