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>

drivers/net/gianfar.c

@@ -1185,7 +1185,7 @@ static int gfar_change_mtu(struct net_device *dev, int new_mtu)
 	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;