netlink: spec: add shaper YAML spec

netlink: spec: add shaper YAML spec

Define the user-space visible interface to query, configure and delete
network shapers via yaml definition.

Add dummy implementations for the relevant NL callbacks.

set() and delete() operations touch a single shaper creating/updating or
deleting it.
The group() operation creates a shaper's group, nesting multiple input
shapers under the specified output shaper.

Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Link: https://patch.msgid.link/7a33a1ff370bdbcd0cd3f909575c912cd56f41da.1728460186.git.pabeni@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>