This introduces set of functions used on server side to account statistics
of RDMA data sent/received.

Link: https://lore.kernel.org/r/20200511135131.27580-12-danil.kipnis@cloud.ionos.comSigned-off-by: NDanil Kipnis <danil.kipnis@cloud.ionos.com>
Signed-off-by: NJack Wang <jinpu.wang@cloud.ionos.com>
Signed-off-by: NJason Gunthorpe <jgg@mellanox.com>