doc/netlink/specs: Update the tc spec

Fill in many of the gaps in the tc netlink spec, including stats attrs,
classes and actions. Many documentation strings have also been added.

This is still a work in progress, albeit fairly complete:
 - there are still many attributes left as binary blobs.
 - actions have not had much testing

Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20240129223458.52046-14-donald.hunter@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>