IB/core: Introduce Receive Work Queue indirection table

Introduce Receive Work Queue (WQ) indirection table.
This object can be used to spread incoming traffic to different
receive Work Queues.

A Receive WQ indirection table points to variable size of WQs.
This table is given to a QP in downstream patches.

Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Matan Barak <matanb@mellanox.com>
Reviewed-by: Sagi Grimberg <sagi@grimerg.me>
Signed-off-by: Doug Ledford <dledford@redhat.com>