igb: Alternate MAC Address Updates for Func2&3

Only function 1 has support for Alternate MAC Address in the EEPROM before,
this update now allow function 2 and 3 to have support for Alternate MAC
Address in the EEPROM.

Signed-off-by: "Akeem G. Abodunrin" <akeem.g.abodunrin@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>