sky2: fix skb truesize underestimation

sky2 allocates a page per skb fragment. We must account
PAGE_SIZE increments on skb->truesize, not the actual frag length.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/marvell/sky2.c b/drivers/net/ethernet/marvell/sky2.c
index 6895e3b..9263490 100644
--- a/drivers/net/ethernet/marvell/sky2.c
+++ b/drivers/net/ethernet/marvell/sky2.c
@@ -2486,7 +2486,7 @@
 
 			frag->size = size;
 			skb->data_len += size;
-			skb->truesize += size;
+			skb->truesize += PAGE_SIZE;
 			skb->len += size;
 			length -= size;
 		}