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>

Author: kuba-moo

Documentation/networking/ethtool-netlink.rst

@@ -2451,7 +2451,7 @@ are netlink only.
   ``ETHTOOL_SRXNTUPLE``               n/a
   ``ETHTOOL_GRXNTUPLE``               n/a
   ``ETHTOOL_GSSET_INFO``              ``ETHTOOL_MSG_STRSET_GET``
-  ``ETHTOOL_GRXFHINDIR``              n/a
+  ``ETHTOOL_GRXFHINDIR``              ``ETHTOOL_MSG_RSS_GET``
   ``ETHTOOL_SRXFHINDIR``              n/a
   ``ETHTOOL_GFEATURES``               ``ETHTOOL_MSG_FEATURES_GET``
   ``ETHTOOL_SFEATURES``               ``ETHTOOL_MSG_FEATURES_SET``