e1000e: add Tx timeout factor for 100Mbps

On some devices (e.g. 82578) not having a Tx timeout factor when linked at
100Mbps can cause false reports of hardware hangs on busy hubs.
Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/e1000e/netdev.c

@@ -3627,7 +3627,7 @@ static void e1000_watchdog_task(struct work_struct *work)
 			case SPEED_100:
 				txb2b = 0;
 				netdev->tx_queue_len = 100;
-				/* maybe add some timeout factor ? */
+				adapter->tx_timeout_factor = 10;
 				break;
 			}