net/hns3: fix configuring RSS hash when rules are flushed

net/hns3: fix configuring RSS hash when rules are flushed

Currently, when performing test case as follow:
1. Run testpmd application based on hns3 network engine with multiple
   receive queues(--rxq=N --txq=N, N>1).
2. Create the special RSS rules by "create flow ..." command in the
   command prompt of the testpmd application.
3. Flush the RSS rules created in step 2 by "flow flush ..." command.
4. Enable RSS by "port config all rss all" command.
In step 4, the command exeuctes successfully. This phenomenon is
inconsistent with the expectation. The API function named
rte_eth_dev_rss_hash_update called in the command should return error
and the command should fail.

This patch fixes it by adding a flag for disabling RSS in the driver.
When RSS rules is flushed, we set the the flag with true, and the
'.rss_hash_update' ops implementation function named
hns3_dev_rss_hash_update return -EINVAL.

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>