IB/core: Add Cisco usNIC rdma node and transport types

This patch adds new rdma node and new rdma transport, and supporting
code used by Cisco's low latency driver called usNIC.  usNIC uses its
own transport, distinct from IB and iWARP.

Signed-off-by: Upinder Malhi <umalhi@cisco.com>
Signed-off-by: Jeff Squyres <jsquyres@cisco.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>