netfilter: Add nf_hook_state initializer function.

This way we can consolidate where we setup new nf_hook_state objects,
to make sure the entire thing is initialized.

The only other place an nf_hook_object is instantiated is nf_queue,
wherein a structure copy is used.

Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc include/linux/netfilter.h
Simple merge