netfilter: nat: remove rcu_read_lock in __nf_nat_decode_session.

__nf_nat_decode_session is called from nf_nat_decode_session as decodefn.
before calling decodefn, it already set rcu_read_lock. so rcu_read_lock in
__nf_nat_decode_session can be removed.
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_nat_core.c

@@ -71,11 +71,10 @@ static void __nf_nat_decode_session(struct sk_buff *skb, struct flowi *fl)
 	if (ct == NULL)
 		return;
 
-	family = ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.l3num;
-	rcu_read_lock();
+	family = nf_ct_l3num(ct);
 	l3proto = __nf_nat_l3proto_find(family);
 	if (l3proto == NULL)
-		goto out;
+		return;
 
 	dir = CTINFO2DIR(ctinfo);
 	if (dir == IP_CT_DIR_ORIGINAL)
@@ -84,8 +83,6 @@ static void __nf_nat_decode_session(struct sk_buff *skb, struct flowi *fl)
 		statusbit = IPS_SRC_NAT;
 
 	l3proto->decode_session(skb, ct, dir, statusbit, fl);
-out:
-	rcu_read_unlock();
 }
 
 int nf_xfrm_me_harder(struct net *net, struct sk_buff *skb, unsigned int family)