ethtool: netlink: simplify arguments to ethnl_default_parse()

Pass struct genl_info directly instead of its members.

Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20230814214723.2924989-10-kuba@kernel.org


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