This change aims to simplify the logic we use to determine WOL
support by reading the EEPROM bits for MACs X540 and newer.

Also some cleanups in ixgbe_wol_supported() - changed return type to
bool and removed redundant return variable by simply using return after
the checks.
Signed-off-by: NEmil Tantilov <emil.s.tantilov@intel.com>
Tested-by: NAndrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>