RDMA/core: RDMA/mlx5: replace use of system_unbound_wq with system_dfl_wq

Currently if a user enqueue a work item using schedule_delayed_work() the
used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use
WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to
schedule_work() that is using system_wq and queue_work(), that makes use
again of WORK_CPU_UNBOUND.

This lack of consistency cannot be addressed without refactoring the API.

system_unbound_wq should be the default workqueue so as not to enforce
locality constraints for random work whenever it's not required.

Adding system_dfl_wq to encourage its use when unbound work should be used.

The old system_unbound_wq will be kept for a few release cycles.

Suggested-by: Tejun Heo <[e-mail]>
Signed-off-by: Marco Crivellari <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Leon Romanovsky <[e-mail]>

drivers/infiniband/core/ucma.c

···
 	if (event->event == RDMA_CM_EVENT_DEVICE_REMOVAL) {
 		xa_lock(&ctx_table);
 		if (xa_load(&ctx_table, ctx->id) == ctx)
-			queue_work(system_unbound_wq, &ctx->close_work);
+			queue_work(system_dfl_wq, &ctx->close_work);
 		xa_unlock(&ctx_table);
 	}
 	return 0;

drivers/infiniband/hw/mlx5/odp.c

···
 
 	/* Freeing a MR is a sleeping operation, so bounce to a work queue */
 	INIT_WORK(&mr->odp_destroy.work, free_implicit_child_mr_work);
-	queue_work(system_unbound_wq, &mr->odp_destroy.work);
+	queue_work(system_dfl_wq, &mr->odp_destroy.work);
 }
 
 static bool mlx5_ib_invalidate_range(struct mmu_interval_notifier *mni,
···
 		destroy_prefetch_work(work);
 		return rc;
 	}
-	queue_work(system_unbound_wq, &work->work);
+	queue_work(system_dfl_wq, &work->work);
 	return 0;
 }