netlink: specs: rtnetlink: correct notify properties

The notify property should point at the object the notifications
carry, usually the get object, not the cmd which triggers
the notification:

  notify:
    description: Name of the command sharing the reply type with
                 this notification.

Not treating this as a fix, I think that only C codegen cares.

Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://patch.msgid.link/20250418021706.1967583-12-kuba@kernel.org


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