igb: cherry-pick fix for link negotation (LP #865523)

[dann frazier]

Please cherry-pick this change into the oneiric kernel:

commit 2c670b5bd794ef93c81bf8797b7d6393c8453fc6
Author: Carolyn Wyborny <carolyn.wyborny at intel.com>
Date:   Tue May 24 06:52:51 2011 +0000

    igb: Add support of SerDes Forced mode for certain hardware
    
    This patch changes the serdes link code to support a forced mode for
    some hardware, based on bit set in EEPROM.
    
    Signed-off-by: Carolyn Wyborny <carolyn.wyborny at intel.com>
    Tested-by: Jeff Pieper <jeffrey.e.pieper at intel.com>
    Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher at intel.com>