e1000e: suggest a possible workaround to a device hang on 82577/8

There is a known issue in the 82577 and 82578 device that can cause a hang
in the device hardware during traffic stress; the current workaround in the
driver is to disable transmit flow control by default.  If the user enables
transmit flow control and the device hang occurs, provide a message in the
syslog suggesting to re-enable the workaround.
Signed-off-by: NBruce Allan <bruce.w.allan@intel.com>
Tested-by: NJeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/e1000e/netdev.c

@@ -1084,6 +1084,10 @@ static void e1000_print_hw_hang(struct work_struct *work)
 	      phy_1000t_status,
 	      phy_ext_status,
 	      pci_status);
+
+	/* Suggest workaround for known h/w issue */
+	if ((hw->mac.type == e1000_pchlan) && (er32(CTRL) & E1000_CTRL_TFCE))
+		e_err("Try turning off Tx pause (flow control) via ethtool\n");
 }
 
 /**