igb: Add stats output for OS2BMC feature on i350 devices

This patch adds statistics output for OS2BMC feature which is configured
by eeprom on capable devices.

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>