tools: ynl-gen: support using dump types for ntf

Classic Netlink has GET callbacks with no doit support, just dumps.
Support using their responses in notifications. If notification points
at a type which only has a dump - use the dump's type.

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/20250429154704.2613851-6-kuba@kernel.org


Signed-off-by: Paolo Abeni <pabeni@redhat.com>