drivers: net: use skb_headlen()

replaces (skb->len - skb->data_len) occurrences by skb_headlen(skb)

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/tehuti.c b/drivers/net/tehuti.c
index a38aede..e29f495 100644
--- a/drivers/net/tehuti.c
+++ b/drivers/net/tehuti.c
@@ -1508,7 +1508,7 @@
 	int nr_frags = skb_shinfo(skb)->nr_frags;
 	int i;
 
-	db->wptr->len = skb->len - skb->data_len;
+	db->wptr->len = skb_headlen(skb);
 	db->wptr->addr.dma = pci_map_single(priv->pdev, skb->data,
 					    db->wptr->len, PCI_DMA_TODEVICE);
 	pbl->len = CPU_CHIP_SWAP32(db->wptr->len);