net: Fix GRO_HASH_BUCKETS assertion.

FIELD_SIZEOF() is in bytes, but we want bits.

Fixes: d9f37d01e294 ("net: convert gro_count to bitmask")
Suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -9282,7 +9282,7 @@ static struct hlist_head * __net_init netdev_create_hash(void)
 static int __net_init netdev_init(struct net *net)
 {
 	BUILD_BUG_ON(GRO_HASH_BUCKETS >
-			FIELD_SIZEOF(struct napi_struct, gro_bitmask));
+		     8 * FIELD_SIZEOF(struct napi_struct, gro_bitmask));
 
 	if (net != &init_net)
 		INIT_LIST_HEAD(&net->dev_base_head);