Merge branch 'ethtool-fail-with-error-if-request-has-unknown-flags'

Michal Kubecek says:

====================
ethtool: fail with error if request has unknown flags

Jakub Kicinski pointed out that if unrecognized flags are set in netlink
header request, kernel shoud fail with an error rather than silently
ignore them so that we have more freedom in future flags semantics.

To help userspace with handling such errors, inform the client which
flags are supported by kernel. For that purpose, we need to allow
passing cookies as part of extack also in case of error (they can be
only passed on success now).
====================

Signed-off-by: David S. Miller <davem@davemloft.net>