IB: IP address based RDMA connection manager

Kernel connection management agent over InfiniBand that connects based
on IP addresses.  The agent defines a generic RDMA connection
abstraction to support clients wanting to connect over different RDMA
devices.

The agent also handles RDMA device hotplug events on behalf of clients.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>