udp_tunnel: Pass UDP socket down through udp_tunnel{, 6}_xmit_skb().

That was we can make sure the output path of ipv4/ipv6 operate on
the UDP socket rather than whatever random thing happens to be in
skb->sk.

Based upon a patch by Jiri Pirko.

Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
diff --git a/net/ipv6/output_core.c b/net/ipv6/output_core.c
index 7d1131d..85892af 100644
--- a/net/ipv6/output_core.c
+++ b/net/ipv6/output_core.c
@@ -136,7 +136,7 @@
 EXPORT_SYMBOL(ip6_dst_hoplimit);
 #endif
 
-int __ip6_local_out(struct sk_buff *skb)
+static int __ip6_local_out_sk(struct sock *sk, struct sk_buff *skb)
 {
 	int len;
 
@@ -146,19 +146,30 @@
 	ipv6_hdr(skb)->payload_len = htons(len);
 	IP6CB(skb)->nhoff = offsetof(struct ipv6hdr, nexthdr);
 
-	return nf_hook(NFPROTO_IPV6, NF_INET_LOCAL_OUT, skb->sk, skb,
+	return nf_hook(NFPROTO_IPV6, NF_INET_LOCAL_OUT, sk, skb,
 		       NULL, skb_dst(skb)->dev, dst_output_sk);
 }
+
+int __ip6_local_out(struct sk_buff *skb)
+{
+	return __ip6_local_out_sk(skb->sk, skb);
+}
 EXPORT_SYMBOL_GPL(__ip6_local_out);
 
-int ip6_local_out(struct sk_buff *skb)
+int ip6_local_out_sk(struct sock *sk, struct sk_buff *skb)
 {
 	int err;
 
-	err = __ip6_local_out(skb);
+	err = __ip6_local_out_sk(sk, skb);
 	if (likely(err == 1))
-		err = dst_output(skb);
+		err = dst_output_sk(sk, skb);
 
 	return err;
 }
+EXPORT_SYMBOL_GPL(ip6_local_out_sk);
+
+int ip6_local_out(struct sk_buff *skb)
+{
+	return ip6_local_out_sk(skb->sk, skb);
+}
 EXPORT_SYMBOL_GPL(ip6_local_out);