e1000: remove e1000_clean_tx_irq call from e1000_netpoll

The call to e1000_clean_tx_irq in e1000_netpoll can race with the call
to e1000_clean_tx_irq in e1000_clean.  With a small bit of tweaking to
to netpoll_send_skb to simulate a system that was under extreme stress,
I was able to reproduce these concurrent calls.  This can result in
multiple frees to the skbs on the tx ring buffer.

Dropping this call from e1000_netpoll should be fine since we can rely
on the calls in e1000_clean to do what is needed since napi will poll
the hardware just after calling poll_controller.
Signed-off-by: Andy Gospodarek <andy@greyhouse.net>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/net/e1000/e1000_main.c

@@ -5251,7 +5251,6 @@ e1000_netpoll(struct net_device *netdev)
 
 	disable_irq(adapter->pdev->irq);
 	e1000_intr(adapter->pdev->irq, netdev);
-	e1000_clean_tx_irq(adapter, adapter->tx_ring);
 #ifndef CONFIG_E1000_NAPI
 	adapter->clean_rx(adapter, adapter->rx_ring);
 #endif