e1000e: stop unnecessary polling when using msi-x

The last hunk of this commit:

    commit 12d04a3c12b420f23398b4d650127642469a60a6
    Author: Alexander Duyck <alexander.h.duyck@intel.com>
    Date:   Wed Mar 25 22:05:03 2009 +0000

        e1000e: commonize tx cleanup routine to match e1000 & igb

changed the logic for determining if we should call napi_complete or
not at then end of a napi poll.

If the NIC is using MSI-X with no work to do in ->poll, net_rx_action
can just spin indefinitely on older kernels and for 2 jiffies on newer
kernels since napi_complete is never called and budget isn't
decremented.

Discovered and verified while testing driver backport to an older
kernel.

Signed-off-by: Andy Gospodarek <andy@greyhouse.net>
Acked-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/e1000e/netdev.c

@@ -1997,7 +1997,7 @@ static int e1000_clean(struct napi_struct *napi, int budget)
 	struct e1000_adapter *adapter = container_of(napi, struct e1000_adapter, napi);
 	struct e1000_hw *hw = &adapter->hw;
 	struct net_device *poll_dev = adapter->netdev;
-	int tx_cleaned = 0, work_done = 0;
+	int tx_cleaned = 1, work_done = 0;
 
 	adapter = netdev_priv(poll_dev);