net/sfc: allow to query RSS key and HF when RSS is disabled

net/sfc: allow to query RSS key and HF when RSS is disabled

If global RSS is not enabled in the multiqueue mode setting,
it will not be possible to change RSS configuration. However,
querying default RSS settings should be possible in any case since
it may be needed by RTE flow API users to find out what RSS settings
will be used by default for a flow rule with RSS action if custom
RSS key and hash function choice are not specified.

Fixes: 63ab5e0c8fda ("net/sfc: use zero RSS channels as disabled RSS indicator")
Cc: stable@dpdk.org
Signed-off-by: Ivan Malov <ivan.malov@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>