Merge branch 'tools-ynl-more-docs-and-basic-ethtool-support'

Jakub Kicinski says:

====================
tools: ynl: more docs and basic ethtool support

I got discouraged from supporting ethtool in specs, because
generating the user space C code seems a little tricky.
The messages are ID'ed in a "directional" way (to and from
kernel are separate ID "spaces"). There is value, however,
in having the spec and being able to for example use it
in Python.

After paying off some technical debt - add a partial
ethtool spec. Partial because the header for ethtool is almost
a 1000 LoC, so converting in one sitting is tough. But adding
new commands should be trivial now.

Last but not least I add more docs, I realized that I've been
sending a similar "instructions" email to people working on
new families. It's now intro-specs.rst.
====================

Link: https://lore.kernel.org/r/20230131023354.1732677-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>