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/ipv4/geneve.c b/net/ipv4/geneve.c
index e64f8e9..b77f5e8 100644
--- a/net/ipv4/geneve.c
+++ b/net/ipv4/geneve.c
@@ -136,7 +136,7 @@
 
 	skb_set_inner_protocol(skb, htons(ETH_P_TEB));
 
-	return udp_tunnel_xmit_skb(rt, skb, src, dst,
+	return udp_tunnel_xmit_skb(rt, gs->sock->sk, skb, src, dst,
 				   tos, ttl, df, src_port, dst_port, xnet,
 				   !csum);
 }