This commit extends the RDMA user ABI to support the flush
operation defined in IBA A19.4.1. These changes are
backward compatible with the existing RDMA user ABI.

Link: https://lore.kernel.org/r/20221206130201.30986-2-lizhijian@fujitsu.comReviewed-by: NZhu Yanjun <zyjzyj2000@gmail.com>
Signed-off-by: NLi Zhijian <lizhijian@fujitsu.com>
Signed-off-by: NJason Gunthorpe <jgg@nvidia.com>