igb: Fix for Alt MAC Address feature on 82580 and later devices

In 82580 and later devices, the alternate MAC address feature is
completely handled by the option ROM and software does not handle
it anymore.  This patch changes the check_alt_mac_addr function to
exit immediately if device is 82580 or later.

Signed-off-by: Carolyn Wyborny <carolyn.wyborny@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>