gianfar: Fix BD_LENGTH_MASK definition

BD_LENGTH_MASK is supposed to catch the low 16-bits of the status field, not
the low byte.  The old way, we would never be able to clean up tx packets with
sizes divisible by 256.
Signed-off-by: NAndy Fleming <afleming@freescale.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/gianfar.h

@@ -312,7 +312,7 @@ extern const char gfar_driver_version[];
 #define ATTRELI_EI(x) (x)
 
 #define BD_LFLAG(flags) ((flags) << 16)
-#define BD_LENGTH_MASK		0x00ff
+#define BD_LENGTH_MASK		0x0000ffff
 
 /* TxBD status field bits */
 #define TXBD_READY		0x8000