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>

drivers/net/ethernet/marvell/sky2.c

@@ -2486,7 +2486,7 @@ static void skb_put_frags(struct sk_buff *skb, unsigned int hdr_space,
 
 			frag->size = size;
 			skb->data_len += size;
-			skb->truesize += size;
+			skb->truesize += PAGE_SIZE;
 			skb->len += size;
 			length -= size;
 		}