netfilter: reset netfilter state when duplicating packet

We should also toss nf_bridge_info, if any -- packet is leaving via
ip_local_out, also, this skb isn't bridged -- it is a locally generated
copy.  Also this avoids the need to touch this later when skb->nfct is
replaced with 'unsigned long _nfct' in followup patch.

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