netfilter: ipv6: Preserve link scope traffic original oif
When ip6_route_me_harder is invoked, it resets outgoing interface of:
- link-local scoped packets sent by neighbor discovery
- multicast packets sent by MLD host
- multicast packets send by MLD proxy daemon that sets outgoing
interface through IPV6_PKTINFO ipi6_ifindex
Link-local and multicast packets must keep their original oif after
ip6_route_me_harder is called.
Signed-off-by: Alin Nastac <alin.nastac@gmail.com> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>