tools: ynl-gen: support excluding tricky ops

The ethtool family has a small handful of quite tricky ops
and a lot of simple very useful ops. Teach ynl-gen to skip
ops so that we can bypass the tricky ones.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>