netfilter: bridge: pass L2 header and VLAN as netlink attributes in queues to userspace

- This creates 2 netlink attribute NFQA_VLAN and NFQA_L2HDR.
- These are filled up for the PF_BRIDGE family on the way to userspace.
- NFQA_VLAN is a nested attribute, with the NFQA_VLAN_PROTO and the
  NFQA_VLAN_TCI carrying the corresponding vlan_proto and vlan_tci
  fields from the skb using big endian ordering (and using the CFI
  bit as the VLAN_TAG_PRESENT flag in vlan_tci as in the skb)

Signed-off-by: Stephane Bryant <stephane.ml.bryant@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>