This is called from the packet input path, we get lock contention
if many cpus handle ipsec in parallel.

After recent rcu conversion it is safe to call __xfrm_state_lookup
without the spinlock.
Signed-off-by: NFlorian Westphal <fw@strlen.de>
Signed-off-by: NSteffen Klassert <steffen.klassert@secunet.com>