nvme-rdma: Don't leak uninitialized memory in connect request private data

Zero out the full nvme_rdma_cm_req structure before sending it.
Otherwise we end up leaking kernel memory in the reserved field, which
might break forward compatibility in the future.

Signed-off-by: Roland Dreier <roland@purestorage.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>