e1000: unify WoL capability detection code

WoL is constantly giving problems and needed a rewrite. Consolidates
all WoL capabilities into a single function, and disables WoL for all
other ports on the device except for port A.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>