Merge branch 'tools-net-ynl-add-sub-message-support-to-ynl'

Donald Hunter says:

====================
tools/net/ynl: Add 'sub-message' support to ynl

This patchset adds a 'sub-message' attribute type to the netlink-raw
schema and implements it in ynl. This provides support for kind-specific
options attributes as used in rt_link and tc raw netlink families.

A description of the new 'sub-message' attribute type and the
corresponding sub-message definitions is provided in patch 3.

The patchset includes updates to the rt_link spec and a new tc spec that
make use of the new 'sub-message' attribute type.

As mentioned in patch 4, encode support is not yet implemented in ynl
and support for sub-message selectors at a different nest level from the
key attribute is not yet supported. I plan to work on these in follow-up
patches.

Patches 1 is code cleanup in ynl
Patches 2-4 add sub-message support to the schema and ynl with
documentation updates.
Patch 5 adds binary and pad support to structs in netlink-raw.
Patches 6-8 contain specs that use the sub-message attribute type.
Patches 9-13 update ynl-gen-rst and its make target
====================

Link: https://lore.kernel.org/r/20231215093720.18774-1-donald.hunter@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>