netfilter: nfnetlink_log: add support for VLAN information

Currently, there is no vlan information (e.g. when used with a vlan aware
bridge) passed to userspache, HWHEADER will contain an 08 00 (ip) suffix
even for tagged ip packets.

Therefore, add an extra netlink attribute that passes the vlan information
to userspace similarly to 15824ab2

 for nfqueue.

Signed-off-by: Michael Braun <michael-dev@fami-braun.de>
Reviewed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>