tools: ynl-gen: support CRUD-like notifications for classic Netlink

tools: ynl-gen: support CRUD-like notifications for classic Netlink

Allow CRUD-style notification where the notification is more
like the response to the request, which can optionally be
looped back onto the requesting socket. Since the notification
and request are different ops in the spec, for example:

    -
      name: delrule
      doc: Remove an existing FIB rule
      attribute-set: fib-rule-attrs
      do:
        request:
          value: 33
          attributes: *fib-rule-all
    -
      name: delrule-ntf
      doc: Notify a rule deletion
      value: 33
      notify: getrule

We need to find the request by ID. Ideally we'd detect this model
from the spec properties, rather than assume that its what all
classic netlink families do. But maybe that'd cause this model
to spread and its easy to get wrong. For now assume CRUD == classic.

Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Link: https://patch.msgid.link/20250429154704.2613851-7-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>