virtio_net: return already tracked tx_fifo_errors via virtnet_getstats()

Tx_fifo_errors are tracked in start_xmit_ for virtio_net, but not
reported in the tallies returned by virtnet_stats().  Return them
as the rx "sub-stats" rx_length_errors and rx_frame_errors are.
Signed-off-by: Rick Jones <rick.jones2@hp.com>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/virtio_net.c

@@ -700,6 +700,7 @@ static struct rtnl_link_stats64 *virtnet_stats(struct net_device *dev,
 	}
 
 	tot->tx_dropped = dev->stats.tx_dropped;
+	tot->tx_fifo_errors = dev->stats.tx_fifo_errors;
 	tot->rx_dropped = dev->stats.rx_dropped;
 	tot->rx_length_errors = dev->stats.rx_length_errors;
 	tot->rx_frame_errors = dev->stats.rx_frame_errors;