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/ixgbevf/ixgbevf_main.c b/drivers/net/ixgbevf/ixgbevf_main.c
index 960e985..f484161 100644
--- a/drivers/net/ixgbevf/ixgbevf_main.c
+++ b/drivers/net/ixgbevf/ixgbevf_main.c
@@ -604,7 +604,7 @@
 		 * packets not getting split correctly
 		 */
 		if (staterr & IXGBE_RXD_STAT_LB) {
-			u32 header_fixup_len = skb->len - skb->data_len;
+			u32 header_fixup_len = skb_headlen(skb);
 			if (header_fixup_len < 14)
 				skb_push(skb, header_fixup_len);
 		}