nvme: fix regression when disconnect a recovering ctrl

We encountered a problem that the disconnect command hangs.
After analyzing the log and stack, we found that the triggering
process is as follows:
CPU0                          CPU1
                                nvme_rdma_error_recovery_work
                                  nvme_rdma_teardown_io_queues
nvme_do_delete_ctrl                 nvme_stop_queues
  nvme_remove_namespaces
  --clear ctrl->namespaces
                                    nvme_start_queues
                                    --no ns in ctrl->namespaces
    nvme_ns_remove                  return(because ctrl is deleting)
      blk_freeze_queue
        blk_mq_freeze_queue_wait
        --wait for ns to unquiesce to clean infligt IO, hang forever

This problem was not found in older kernels because we will flush
err work in nvme_stop_ctrl before nvme_remove_namespaces.It does not
seem to be modified for functional reasons, the patch can be revert
to solve the problem.

Revert commit 794a4cb3 ("nvme: remove the .stop_ctrl callout")

Signed-off-by: Ruozhu Li <liruozhu@huawei.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>