gianfar: Fix frame size calculation when hardware VLAN acceleration is on

In gfar_change_mtu(), the frame size needs to be increased to account
for the extra 4 bytes VLAN adds to the ethernet header.  However,
it was being increased by the length of the whole header (18 bytes),
which is wrong.

Signed-off-by: Dai Haruki <dai.haruki@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/drivers/net/gianfar.c b/drivers/net/gianfar.c
index 718cf77..0ab4b26 100644
--- a/drivers/net/gianfar.c
+++ b/drivers/net/gianfar.c
@@ -1185,7 +1185,7 @@
 	int frame_size = new_mtu + ETH_HLEN;
 
 	if (priv->vlan_enable)
-		frame_size += VLAN_ETH_HLEN;
+		frame_size += VLAN_HLEN;
 
 	if (gfar_uses_fcb(priv))
 		frame_size += GMAC_FCB_LEN;