Get a list of RDMA devices currently available.
struct ibv_context ** rdma_get_devices
If non-NULL, set to the number of devices returned.
Return a NULL-terminated array of opened RDMA devices. Callers can use
this routine to allocate resources on specific RDMA devices that will be
shared across multiple rdma_cm_id's.
Returns an array of available RDMA devices, or NULL if the request
fails. On failure, errno will be set to indicate the failure reason.
The returned array must be released by calling rdma_free_devices. Devices
remain opened while the librdmacm is loaded.