doc: ethtool: mark ETHTOOL_GRXFHINDIR as reimplemented

The ETHTOOL_GRXFHINDIR reimplementation has been completed around
a year ago. We have been tweaking it so a bit hard to point
to a single commit that completed it, but all the fields available
in IOCTL are reported via Netlink.

Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://patch.msgid.link/20250623231720.3124717-8-kuba@kernel.org


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