RDMA/rtrs: core: lib functions shared between client and server modules

This is a set of library functions existing as a rtrs-core module, used by
client and server modules.

Mainly these functions wrap IB and RDMA calls and provide a bit higher
abstraction for implementing of RTRS protocol on client or server sides.

Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Danil Kipnis <[email protected]>
Signed-off-by: Jack Wang <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>

Author: Jack Wang