netfilter: nf_queue: place bridge physports into queue_entry struct

The refcount is done via entry->skb, which does work fine.
Major problem: When putting the refcount of the bridge ports, we
must always put the references while the skb is still around.

However, we will need to put the references after okfn() to avoid
a possible 1 -> 0 -> 1 refcount transition, so we cannot use the
skb pointer anymore.

Place the physports in the queue entry structure instead to allow
for refcounting changes in the next patch.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>