igb: Supported and Advertised Pause Frame

This patch add ethtool supports for Supported and Advertised Pause Frame,
based on Adapter Flow Control settings.

Signed-off-by: Akeem G. Abodunrin <akeem.g.abodunrin@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>