net/sfc: fix RSS hash offload if queue action is used

net/sfc: fix RSS hash offload if queue action is used

When RSS hash offload is requested, the ingress filters that forward
packets to an RX queue must have an RSS context assigned to them to
calculate RSS hash, which was not always provided.

Fix it by creating a dummy RSS context that forwards packets
to the same queue and assign it to created by flow API filters when
RSS hash offload is enabled. RSS key and hash functions from
default RSS context are used.

Fixes: 5d308972954c ("ethdev: add mbuf RSS update as an offload")
Cc: stable@dpdk.org
Signed-off-by: Igor Romanov <igor.romanov@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>