e1000e: NIC goes up and immediately goes down

commit b7ec70be upstream.

Found that commit d478eb44 was a bad commit.
If the link partner is transmitting codeword (even if NULL codeword),
then the RXCW.C bit will be set so check for RXCW.CW is unnecessary.
Ref: RH BZ 840642
Reported-by: Fabio Futigami <ffutigam@redhat.com>
Signed-off-by: Tushar Dave <tushar.n.dave@intel.com>
CC: Marcelo Ricardo Leitner <mleitner@redhat.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/net/ethernet/intel/e1000e/82571.c

@@ -1600,10 +1600,8 @@ static s32 e1000_check_for_serdes_link_82571(struct e1000_hw *hw)
 			 * auto-negotiation in the TXCW register and disable
 			 * forced link in the Device Control register in an
 			 * attempt to auto-negotiate with our link partner.
-			 * If the partner code word is null, stop forcing
-			 * and restart auto negotiation.
 			 */
-			if ((rxcw & E1000_RXCW_C) || !(rxcw & E1000_RXCW_CW))  {
+			if (rxcw & E1000_RXCW_C) {
 				/* Enable autoneg, and unforce link up */
 				ew32(TXCW, mac->txcw);
 				ew32(CTRL, (ctrl & ~E1000_CTRL_SLU));