ipv6: gro: fix PV6_GRO_CB(skb)->proto problem

It seems IPV6_GRO_CB(skb)->proto can be destroyed in skb_gro_receive()
if a new skb is allocated (to serve as an anchor for frag_list)

We copy NAPI_GRO_CB() only (not the IPV6 specific part) in :

*NAPI_GRO_CB(nskb) = *NAPI_GRO_CB(p);

So we leave IPV6_GRO_CB(nskb)->proto to 0 (fresh skb allocation) instead
of IPPROTO_TCP (6)

ipv6_gro_complete() isnt able to call ops->gro_complete()
[ tcp6_gro_complete() ]

Fix this by moving proto in NAPI_GRO_CB() and getting rid of
IPV6_GRO_CB

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 0a36fff..561c8bc 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1513,6 +1513,9 @@
 
 	/* jiffies when first packet was created/queued */
 	unsigned long age;
+
+	/* Used in ipv6_gro_receive() */
+	int	proto;
 };
 
 #define NAPI_GRO_CB(skb) ((struct napi_gro_cb *)(skb)->cb)