alloc_workqueue replaces deprecated create_workqueue().

A dedicated workqueue has been used since the workqueue
mlxsw_wq is used for FDB notif. processing with workitems that are
involved in normal device operation && because it's a network device
which can be depended upon during memory reclaim.

Workitems &trans->timeout_dw and &mlxsw_sp->fdb_notify.dw,
map to mlxsw_sp_fdb_notify_work (processes FDB notifications from the
underlying device and resolves the netdev to which the entry points to
and notifies the bridge using the switchdev notifier) and
mlxsw_emad_trans_timeout_work (provides async EMAD register access)
respectively. They require forward progress under memory pressure and
hence, WQ_MEM_RECLAIM has been set.

Since there are only a fixed number of work items, explicit concurrency
limit is unnecessary here.
Signed-off-by: NBhaktipriya Shridhar <bhaktipriya96@gmail.com>
Tested-by: NIdo Schimmel <idosch@mellanox.com>
Acked-by: NJiri Pirko <jiri@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>