net-gro: remove GRO_DROP

GRO_DROP can only be returned from napi_gro_frags()
if the skb has not been allocated by a prior napi_get_frags()

Since drivers must use napi_get_frags() and test its result
before populating the skb with metadata, we can safely remove
GRO_DROP since it offers no practical use.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jesse Brandeburg <jesse.brandeburg@intel.com>
Acked-by: Edward Cree <ecree.xilinx@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/netdevice.h

@@ -376,7 +376,6 @@ enum gro_result {
 	GRO_MERGED_FREE,
 	GRO_HELD,
 	GRO_NORMAL,
-	GRO_DROP,
 	GRO_CONSUMED,
 };
 typedef enum gro_result gro_result_t;

net/core/dev.c

@@ -6070,10 +6070,6 @@ static gro_result_t napi_skb_finish(struct napi_struct *napi,
 		gro_normal_one(napi, skb);
 		break;
 
-	case GRO_DROP:
-		kfree_skb(skb);
-		break;
-
 	case GRO_MERGED_FREE:
 		if (NAPI_GRO_CB(skb)->free == NAPI_GRO_FREE_STOLEN_HEAD)
 			napi_skb_free_stolen_head(skb);
@@ -6158,10 +6154,6 @@ static gro_result_t napi_frags_finish(struct napi_struct *napi,
 			gro_normal_one(napi, skb);
 		break;
 
-	case GRO_DROP:
-		napi_reuse_skb(napi, skb);
-		break;
-
 	case GRO_MERGED_FREE:
 		if (NAPI_GRO_CB(skb)->free == NAPI_GRO_FREE_STOLEN_HEAD)
 			napi_skb_free_stolen_head(skb);
@@ -6223,9 +6215,6 @@ gro_result_t napi_gro_frags(struct napi_struct *napi)
 	gro_result_t ret;
 	struct sk_buff *skb = napi_frags_skb(napi);
 
-	if (!skb)
-		return GRO_DROP;
-
 	trace_napi_gro_frags_entry(skb);
 
 	ret = napi_frags_finish(napi, skb, dev_gro_receive(napi, skb));