ethtool: Add GTP RSS hash options to ethtool.h

This is a patch that enables RSS functionality for GTP packets using ethtool.

A user can include TEID and make RSS work for GTP-U over IPv4 by doing the
following:`ethtool -N ens3 rx-flow-hash gtpu4 sde`

In addition to gtpu(4|6), we now support gtpc(4|6),gtpc(4|6)t,gtpu(4|6)e,
gtpu(4|6)u, and gtpu(4|6)d.

gtpc(4|6): Used for GTP-C in IPv4 and IPv6, where the GTP header format does
not include a TEID.
gtpc(4|6)t: Used for GTP-C in IPv4 and IPv6, with a GTP header format that
includes a TEID.
gtpu(4|6): Used for GTP-U in both IPv4 and IPv6 scenarios.
gtpu(4|6)e: Used for GTP-U with extended headers in both IPv4 and IPv6.
gtpu(4|6)u: Used when the PSC (PDU session container) in the GTP-U extended
header includes Uplink, applicable to both IPv4 and IPv6.
gtpu(4|6)d: Used when the PSC in the GTP-U extended header includes Downlink,
for both IPv4 and IPv6.

GTP generates a flow that includes an ID called TEID to identify the tunnel.
This tunnel is created for each UE (User Equipment).By performing RSS based on
this flow, it is possible to apply RSS for each communication unit from the UE.
Without this, RSS would only be effective within the range of IP addresses. For
instance, the PGW can only perform RSS within the IP range of the SGW.
Problematic from a load distribution perspective, especially if there's a bias
in the terminals connected to a particular base station.This case can be
solved by using this patch.

Signed-off-by: Takeru Hayasaka <hayatake396@gmail.com>
Reviewed-by: Marcin Szycik <marcin.szycik@linux.intel.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>