net/hns3: add RSS hash offload to Rx configuration

net/hns3: add RSS hash offload to Rx configuration

Rx offload flag `DEV_RX_OFFLOAD_RSS_HASH` which can be used to
enable/disable PMDs write to `rte_mbuf::hash::rss`. The hns3 PMD driver
already can notify the validity of `rte_mbuf::hash:rss` to the
application by enabling `PKT_RX_RSS_HASH` flag in `rte_mbuf::ol_flags`.

Fixes: 19a3ca4c99cf ("net/hns3: add start/stop and configure operations")
Fixes: c37ca66f2b27 ("net/hns3: support RSS")
Cc: stable@dpdk.org
Signed-off-by: Lijun Ou <oulijun@huawei.com>
Signed-off-by: Wei Hu (Xavier) <xavier.huwei@huawei.com>