tools: ynl: populate most of the ethtool spec

Things that are not implemented:
- cable tests
- bitmaks in the requests don't work (needs multi-attr support in ynl.py)
- stats-get seems to return nonsense (not passing a bitmask properly?)
- notifications are not tested

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>