gro: Open-code frags copy in skb_gro_receive

gcc does a poor job at generating code for the memcpy of the frags
array in skb_gro_receive, which is the primary purpose of that
function when merging frags.  In particular, it can't utilise the
alignment information of the source and destination.  This patch
open-codes the copy so we process words instead of bytes.
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -2673,6 +2673,9 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
 	if (skb_shinfo(p)->frag_list)
 		goto merge;
 	else if (skb_headlen(skb) <= skb_gro_offset(skb)) {
+		skb_frag_t *frag;
+		int i;
+
 		if (skb_shinfo(p)->nr_frags + skb_shinfo(skb)->nr_frags >
 		    MAX_SKB_FRAGS)
 			return -E2BIG;
@@ -2682,9 +2685,9 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
 		skb_shinfo(skb)->frags[0].size -=
 			skb_gro_offset(skb) - skb_headlen(skb);
 
-		memcpy(skb_shinfo(p)->frags + skb_shinfo(p)->nr_frags,
-		       skb_shinfo(skb)->frags,
-		       skb_shinfo(skb)->nr_frags * sizeof(skb_frag_t));
+		frag = skb_shinfo(p)->frags + skb_shinfo(p)->nr_frags;
+		for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
+			*frag++ = skb_shinfo(skb)->frags[i];
 
 		skb_shinfo(p)->nr_frags += skb_shinfo(skb)->nr_frags;
 		skb_shinfo(skb)->nr_frags = 0;