net: ethtool: add an extack parameter to new rxfh_context APIs

Currently passed as NULL, but will allow drivers to report back errors
 when ethnl support for these ops is added.

Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Link: https://patch.msgid.link/6e0012347d175fdd1280363d7bfa76a2f2777e17.1719502240.git.ecree.xilinx@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>