netlink: specs: correct the spec of ethtool

The spec for Ethtool is a bit inaccurate. We don't currently
support dump. Context is only accepted as input and not echoed
to output (which is a separate bug).

Fixes: a353318e ("tools: ynl: populate most of the ethtool spec")
Acked-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Joe Damato <jdamato@fastly.com>
Link: https://patch.msgid.link/20240724234249.2621109-2-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>