iavf: add RSS support for GTP protocol via ethtool

iavf: add RSS support for GTP protocol via ethtool

Extend the iavf driver to support Receive Side Scaling (RSS)
configuration for GTP (GPRS Tunneling Protocol) flows using ethtool.

The implementation introduces new RSS flow segment headers and hash field
definitions for various GTP encapsulations, including:

  - GTPC
  - GTPU (IP, Extension Header, Uplink, Downlink)
  - TEID-based hashing

The ethtool interface is updated to parse and apply these new flow types
and hash fields, enabling fine-grained traffic distribution for GTP-based
mobile workloads.

This enhancement improves performance and scalability for virtualized
network functions (VNFs) and user plane functions (UPFs) in 5G and LTE
deployments.

Reviewed-by: Jedrzej Jagielski <jedrzej.jagielski@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>