gro: Check for GSO packets and packets with frag_list

As GRO cannot be applied to packets with frag_list we need to
make sure that we reject such packets if they are fed to us,
e.g., through a tunnel device.

Also there is no point in applying GRO on GSO packets so they
too should be rejected.  This allows GRO to be used in virtio-net
which may produce GSO packets directly but may still benefit
from GRO if the other end of it doesn't support GSO.
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -2392,6 +2392,9 @@ int dev_gro_receive(struct napi_struct *napi, struct sk_buff *skb)
 	if (!(skb->dev->features & NETIF_F_GRO))
 		goto normal;
 
+	if (skb_is_gso(skb) || skb_shinfo(skb)->frag_list)
+		goto normal;
+
 	rcu_read_lock();
 	list_for_each_entry_rcu(ptype, head, list) {
 		struct sk_buff *p;