igb: do not modify tx_queue_len on link speed change

Previously the driver tweaked txqueuelen to avoid false Tx hang reports seen at half duplex.
This had the effect of overriding user set values on link change/reset. Testing shows that
adjusting only the timeout factor is sufficient to prevent Tx hang reports at half duplex.

Based on e1000e patch by Franco Fichtner <franco@lastsummer.de>

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/igb/igb.h

@@ -267,7 +267,6 @@ struct igb_adapter {
 
 	/* TX */
 	struct igb_ring *tx_ring[16];
-	unsigned long tx_queue_len;
 	u32 tx_timeout_count;
 
 	/* RX */

drivers/net/igb/igb_main.c

@@ -1105,9 +1105,6 @@ static void igb_configure(struct igb_adapter *adapter)
 		struct igb_ring *ring = adapter->rx_ring[i];
 		igb_alloc_rx_buffers_adv(ring, igb_desc_unused(ring));
 	}
-
-
-	adapter->tx_queue_len = netdev->tx_queue_len;
 }
 
 /**
@@ -1213,7 +1210,6 @@ void igb_down(struct igb_adapter *adapter)
 	del_timer_sync(&adapter->watchdog_timer);
 	del_timer_sync(&adapter->phy_info_timer);
 
-	netdev->tx_queue_len = adapter->tx_queue_len;
 	netif_carrier_off(netdev);
 
 	/* record the stats before reset*/
@@ -3106,17 +3102,13 @@ static void igb_watchdog_task(struct work_struct *work)
 			       ((ctrl & E1000_CTRL_RFCE) ?  "RX" :
 			       ((ctrl & E1000_CTRL_TFCE) ?  "TX" : "None")));
 
-			/* tweak tx_queue_len according to speed/duplex and
-			 * adjust the timeout factor */
-			netdev->tx_queue_len = adapter->tx_queue_len;
+			/* adjust timeout factor according to speed/duplex */
 			adapter->tx_timeout_factor = 1;
 			switch (adapter->link_speed) {
 			case SPEED_10:
-				netdev->tx_queue_len = 10;
 				adapter->tx_timeout_factor = 14;
 				break;
 			case SPEED_100:
-				netdev->tx_queue_len = 100;
 				/* maybe add some timeout factor ? */
 				break;
 			}