net: pegasus: Remove deprecated create_singlethread_workqueue

The workqueue "pegasus_workqueue" queues a single work item per pegasus
instance and hence it doesn't require execution ordering. Hence,
alloc_workqueue has been used to replace the deprecated
create_singlethread_workqueue instance.

The WQ_MEM_RECLAIM flag has been set to ensure forward progress under
memory pressure since it's a network driver.

Since there are fixed number of work items, explicit concurrency
limit is unnecessary here.

Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Petko Manolov <petkan@mip-labs.com>
Signed-off-by: David S. Miller <davem@davemloft.net>