veth: Dont kfree_skb() after dev_forward_skb()

In case of congestion, netif_rx() frees the skb, so we must assume
dev_forward_skb() also consume skb.

Bug introduced by commit 445409602c092
(veth: move loopback logic to common location)

We must change dev_forward_skb() to always consume skb, and veth to not
double free it.

Bug report : http://marc.info/?l=linux-netdev&m=127310770900442&w=3

Reported-by: Martín Ferrari <martin.ferrari@gmail.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
__napi_gro_receive(struct napi_struct *napi, struct sk_buff *skb)
{
	struct sk_buff *p;

	if (netpoll_rx_on(skb))
		return GRO_NORMAL;

	for (p = napi->gro_list; p; p = p->next) {
		NAPI_GRO_CB(p)->same_flow =
			(p->dev == skb->dev) &&
			!compare_ether_header(skb_mac_header(p),
					      skb_gro_mac_header(skb));
		NAPI_GRO_CB(p)->flush = 0;
	}

	return dev_gro_receive(napi, skb);
}

__napi_gro_receive(struct napi_struct *napi, struct sk_buff *skb)
{
	struct sk_buff *p;

	if (netpoll_rx_on(skb))
		return GRO_NORMAL;

	for (p = napi->gro_list; p; p = p->next) {
		NAPI_GRO_CB(p)->same_flow =
			(p->dev == skb->dev) &&
			!compare_ether_header(skb_mac_header(p),
					      skb_gro_mac_header(skb));
		NAPI_GRO_CB(p)->flush = 0;
	}

	return dev_gro_receive(napi, skb);
}
