RDMA/hns: Use the reserved loopback QPs to free MR before destroying MPT

mainline inclusion
from mainline-v5.18-rc1
commit 70f92521
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5IZO5
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/rdma/rdma.git/commit/?id=70f92521584f1d1e8268311ee84413307b0fdea8

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Before destroying MPT, the reserved loopback QPs send loopback IOs (one
write operation per SL). Completing these loopback IOs represents that
there isn't any outstanding request in MPT, then it's safe to destroy MPT.

Link: https://lore.kernel.org/r/20220310042835.38634-1-liangwenpeng@huawei.com


Signed-off-by: Yixing Liu <liuyixing1@huawei.com>
Signed-off-by: Wenpeng Liang <liangwenpeng@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Zhengfeng Luo <luozhengfeng@h-partners.com>
Reviewed-by: Yangyang Li <liyangyang20@huawei.com>
Reviewed-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>