ethtool: rss: support setting input-xfrm via Netlink

Support configuring symmetric hashing via Netlink.
We have the flow field config prepared as part of SET handling,
so scan it for conflicts instead of querying the driver again.

Reviewed-by: Gal Pressman <gal@nvidia.com>
Link: https://patch.msgid.link/20250716000331.1378807-10-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>