devlink: move small_ops definition into netlink.c

Move the generic netlink small_ops definition where they are consumed,
into netlink.c

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20230828061657.300667-15-jiri@resnulli.us


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