RDMA/mlx5: Introduce mlx5_umr_post_send_wait()

Introduce mlx5_umr_post_send_wait() that uses a UMR adjusted flow for
posting WQEs. The next patches will gradually move UMR operations to use
this flow. Once done, will get rid of mlx5_ib_post_send_wait().

mlx5_umr_post_send_wait gets already written WQE segments and will only
memcpy it to the SQ. This way, we avoid packing all the data in a WR just
to unpack it into the WQE.

Link: https://lore.kernel.org/r/f027dd592fde62402b2d49efded8d1d22229d22b.1649747695.git.leonro@nvidia.com


Signed-off-by: Aharon Landau <aharonl@nvidia.com>
Reviewed-by: Michael Guralnik <michaelgur@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>