8139cp: reset BQL when ring tx ring cleared

This patch cures transmit timeout's with DHCP observed
while running under KVM. When the transmit ring is cleaned out,
the Byte Queue Limit values need to be reset.
Signed-off-by: NStephen Hemminger <stephen@networkplumber.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/realtek/8139cp.c

@@ -1136,6 +1136,7 @@ static void cp_clean_rings (struct cp_private *cp)
 			cp->dev->stats.tx_dropped++;
 		}
 	}
+	netdev_reset_queue(cp->dev);
 
 	memset(cp->rx_ring, 0, sizeof(struct cp_desc) * CP_RX_RING_SIZE);
 	memset(cp->tx_ring, 0, sizeof(struct cp_desc) * CP_TX_RING_SIZE);