This patch implements SERDES loopback configuration for i210 devices by
unsetting sigdetect bit, so as to fix Ethtool loopback test failure. Old
sigdetect code is also simplified to take care of all devices newer than 82580
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>