This patch unsets the sigdetect bit for SERDES loopback tests on 82580 and
i350 parts.  The loopback test can fail on these parts without this
setting.
Signed-off-by: NCarolyn Wyborny <carolyn.wyborny@intel.com>
Tested-by: NAaron Brown <aaron.f.brown@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>