net-gro: avoid reorders

Receiving a GSO packet in dev_gro_receive() is not uncommon
in stacked devices, or devices partially implementing LRO/GRO
like bnx2x. GRO is implementing the aggregation the device
was not able to do itself.

Current code causes reorders, like in following case :

For a given flow where sender sent 3 packets P1,P2,P3,P4

Receiver might receive P1 as a single packet, stored in GRO engine.

Then P2-P4 are received as a single GSO packet, immediately given to
upper stack, while P1 is held in GRO engine.

This patch will make sure P1 is given to upper stack, then P2-P4
immediately after.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -4482,7 +4482,7 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 	if (!(skb->dev->features & NETIF_F_GRO))
 		goto normal;
 
-	if (skb_is_gso(skb) || skb_has_frag_list(skb) || skb->csum_bad)
+	if (skb->csum_bad)
 		goto normal;
 
 	gro_list_prepare(napi, skb);
@@ -4495,7 +4495,7 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 		skb_set_network_header(skb, skb_gro_offset(skb));
 		skb_reset_mac_len(skb);
 		NAPI_GRO_CB(skb)->same_flow = 0;
-		NAPI_GRO_CB(skb)->flush = 0;
+		NAPI_GRO_CB(skb)->flush = skb_is_gso(skb) || skb_has_frag_list(skb);
 		NAPI_GRO_CB(skb)->free = 0;
 		NAPI_GRO_CB(skb)->encap_mark = 0;
 		NAPI_GRO_CB(skb)->recursion_counter = 0;