iavf: Support for modifying TCP RSS flow hashing

Provides the ability to enable TCP RSS hashing by ethtool.

It gives users option of generating RSS hash based on the TCP 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>