IB/ipoib_verbs: Remove deprecated create_singlethread_workqueue

alloc_ordered_workqueue() with WQ_MEM_RECLAIM set, replaces
deprecated create_singlethread_workqueue(). This is the identity
conversion.

The workqueue "wq" queues mulitple work items viz &priv->restart_task,
&priv->cm.rx_reap_task, &priv->cm.skb_task, &priv->neigh_reap_task,
&priv->ah_reap_task, &priv->mcast_task and &priv->carrier_on_task.
The work items require strict execution ordering.
Hence, an ordered dedicated workqueue has been used.

WQ_MEM_RECLAIM has been set to ensure forward progress under
memory pressure.

Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>