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: Carolyn Wyborny <carolyn.wyborny@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>