[TG3]: add variable buffer size for standard ring

Add a new rx_pkt_buf_sz to the tg3 structure to support variable buffer
sizes on the standard ring.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/tg3.h

@@ -2088,6 +2088,8 @@ struct tg3 {
 	struct tg3_rx_buffer_desc	*rx_rcb;
 	dma_addr_t			rx_rcb_mapping;
 
+	u32				rx_pkt_buf_sz;
+
 	/* begin "everything else" cacheline(s) section */
 	struct net_device_stats		net_stats;
 	struct net_device_stats		net_stats_prev;