sfc: XMAC statistics fix-ups

Exclude assumed size of RX control frames from rx_bad_bytes.

Exclude assumed size of TX control frames from tx_good_bytes for
consistency with rx_good_bytes.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/net/sfc/falcon_xmac.c

@@ -554,9 +554,11 @@ void falcon_update_stats_xmac(struct efx_nic *efx)
 
 	/* Update derived statistics */
 	mac_stats->tx_good_bytes =
-		(mac_stats->tx_bytes - mac_stats->tx_bad_bytes);
+		(mac_stats->tx_bytes - mac_stats->tx_bad_bytes -
+		 mac_stats->tx_control * 64);
 	mac_stats->rx_bad_bytes =
-		(mac_stats->rx_bytes - mac_stats->rx_good_bytes);
+		(mac_stats->rx_bytes - mac_stats->rx_good_bytes -
+		 mac_stats->rx_control * 64);
 }
 
 int falcon_check_xmac(struct efx_nic *efx)