netlink: specs: don't allow version to be specified for genetlink

There is no good reason to specify the version for new protocols.
Forbid it in genetlink schema.

If the future proves me wrong, this restriction could be easily lifted.

Move the version definition in between legacy properties
in genetlink-legacy.

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20231010074810.191177-1-jiri@resnulli.us


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