xfrm: state: make xfrm_state_lookup_byaddr lockless

This appears to be an oversight back when the state lookup
was converted to RCU, I see no reason why we need to hold the
state lock here.

__xfrm_state_lookup_byaddr already uses xfrm_state_hold_rcu
helper to obtain a reference, so just replace the state
lock with rcu.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

Author: Florian Westphal

net/xfrm/xfrm_state.c

@@ -2313,12 +2313,12 @@ xfrm_state_lookup_byaddr(struct net *net, u32 mark,
 	struct xfrm_hash_state_ptrs state_ptrs;
 	struct xfrm_state *x;
 
-	spin_lock_bh(&net->xfrm.xfrm_state_lock);
+	rcu_read_lock();
 
 	xfrm_hash_ptrs_get(net, &state_ptrs);
 
 	x = __xfrm_state_lookup_byaddr(&state_ptrs, mark, daddr, saddr, proto, family);
-	spin_unlock_bh(&net->xfrm.xfrm_state_lock);
+	rcu_read_unlock();
 	return x;
 }
 EXPORT_SYMBOL(xfrm_state_lookup_byaddr);