ixgbe: Add ethtool support to enable 2.5 and 5.0 Gbps support

Added full support for new version Ethtool API. New API allow use
2500Gbase-T and 5000base-T supported and advertised link speed modes.

Signed-off-by: Radoslaw Tyl <radoslawx.tyl@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>