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/forcedeth.c b/drivers/net/forcedeth.c
index 8aa8094..a1c0e7b 100644
--- a/drivers/net/forcedeth.c
+++ b/drivers/net/forcedeth.c
@@ -2148,7 +2148,7 @@
 	unsigned int i;
 	u32 offset = 0;
 	u32 bcnt;
-	u32 size = skb->len-skb->data_len;
+	u32 size = skb_headlen(skb);
 	u32 entries = (size >> NV_TX2_TSO_MAX_SHIFT) + ((size & (NV_TX2_TSO_MAX_SIZE-1)) ? 1 : 0);
 	u32 empty_slots;
 	struct ring_desc* put_tx;
@@ -2269,7 +2269,7 @@
 	unsigned int i;
 	u32 offset = 0;
 	u32 bcnt;
-	u32 size = skb->len-skb->data_len;
+	u32 size = skb_headlen(skb);
 	u32 entries = (size >> NV_TX2_TSO_MAX_SHIFT) + ((size & (NV_TX2_TSO_MAX_SIZE-1)) ? 1 : 0);
 	u32 empty_slots;
 	struct ring_desc_ex* put_tx;