net: ethtool: only allow set_rxnfc with rss + ring_cookie if driver opts in

net: ethtool: only allow set_rxnfc with rss + ring_cookie if driver opts in

Ethtool ntuple filters with FLOW_RSS were originally defined as adding
 the base queue ID (ring_cookie) to the value from the indirection table,
 so that the same table could distribute over more than one set of queues
 when used by different filters.
However, some drivers / hardware ignore the ring_cookie, and simply use
 the indirection table entries as queue IDs directly.  Thus, for drivers
 which have not opted in by setting ethtool_ops.cap_rss_rxnfc_adds to
 declare that they support the original (addition) semantics, reject in
 ethtool_set_rxnfc any filter which combines FLOW_RSS and a nonzero ring.
(For a ring_cookie of zero, both behaviours are equivalent.)
Set the cap bit in sfc, as it is known to support this feature.

Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Reviewed-by: Martin Habets <habetsm.xilinx@gmail.com>
Link: https://patch.msgid.link/cc3da0844083b0e301a33092a6299e4042b65221.1731499022.git.ecree.xilinx@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>