iavf: Support for modifying UDP RSS flow hashing

Provides the ability to enable UDP RSS hashing by ethtool.

It gives users option of generating RSS hash based on the UDP source
and destination ports numbers, IPv4 or IPv6 source and destination
addresses.

Signed-off-by: Haiyue Wang <haiyue.wang@intel.com>
Tested-by: Konrad Jankowski <konrad0.jankowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>