[IPV6]: Fix xfrm tunnel oops with large packets

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/xfrm6_output.c

@@ -84,6 +84,7 @@ static int xfrm6_tunnel_check_size(struct sk_buff *skb)
 		mtu = IPV6_MIN_MTU;
 
 	if (skb->len > mtu) {
+		skb->dev = dst->dev;
 		icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu, skb->dev);
 		ret = -EMSGSIZE;
 	}