cpmac: fix the receiving of 802.1q frames

Despite what the comment above CPMAC_SKB_SIZE says, the hardware also
needs to account for the FCS length in a received frame. This patch fix
the receiving of 802.1q frames which have 4 more bytes. While at it
unhardcode the definition and use the one from if_vlan.h.
Signed-off-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/cpmac.c

@@ -28,6 +28,7 @@
 #include <linux/delay.h>
 
 #include <linux/netdevice.h>
+#include <linux/if_vlan.h>
 #include <linux/etherdevice.h>
 #include <linux/ethtool.h>
 #include <linux/skbuff.h>
@@ -56,8 +57,8 @@ MODULE_PARM_DESC(debug_level, "Number of NETIF_MSG bits to enable");
 MODULE_PARM_DESC(dumb_switch, "Assume switch is not connected to MDIO bus");
 
 #define CPMAC_VERSION "0.5.1"
-/* frame size + 802.1q tag */
-#define CPMAC_SKB_SIZE		(ETH_FRAME_LEN + 4)
+/* frame size + 802.1q tag + FCS size */
+#define CPMAC_SKB_SIZE		(ETH_FRAME_LEN + ETH_FCS_LEN + VLAN_HLEN)
 #define CPMAC_QUEUES	8
 
 /* Ethernet registers */