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/atm/eni.c b/drivers/atm/eni.c
index 719ec5a..90a5a7c 100644
--- a/drivers/atm/eni.c
+++ b/drivers/atm/eni.c
@@ -1131,7 +1131,7 @@
 			if (i == -1)
 				put_dma(tx->index,eni_dev->dma,&j,(unsigned long)
 				    skb->data,
-				    skb->len - skb->data_len);
+				    skb_headlen(skb));
 			else
 				put_dma(tx->index,eni_dev->dma,&j,(unsigned long)
 				    skb_shinfo(skb)->frags[i].page + skb_shinfo(skb)->frags[i].page_offset,