igb: No longer rely on APME to determine WoL settings

Historically, we've been using the APME bit to determine whether a device
supports wake on a given port or not. However, this bit specifies the
default wake setting, rather than the wake support. Change the behavior so
that we use a flag to keep the capabilities separate from the enablement
while meeting customer requirements.

Signed-off-by: Matthew Vick <matthew.vick@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>