net/core/dev: Warn on a too-short GRO frame

When signaling that a GRO frame is ready to be processed, the network stack
correctly checks length and aborts processing when a frame is less than 14
bytes. However, such a condition is really indicative of a broken driver,
and should be loudly signaled, rather than silently dropped as the case is
today.

Convert the condition to use net_warn_ratelimited() to ensure the stack
loudly complains about such broken drivers.
Signed-off-by: Aaron Conole <aconole@bytheb.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -4663,6 +4663,8 @@ static struct sk_buff *napi_frags_skb(struct napi_struct *napi)
 	if (unlikely(skb_gro_header_hard(skb, hlen))) {
 		eth = skb_gro_header_slow(skb, hlen, 0);
 		if (unlikely(!eth)) {
+			net_warn_ratelimited("%s: dropping impossible skb from %s\n",
+					     __func__, napi->dev->name);
 			napi_reuse_skb(napi, skb);
 			return NULL;
 		}