nfsd/sunrpc: abstract out svc_set_num_threads to sv_ops

Add an operation that will do setup of the service. In the case of a
classic thread-based service that means starting up threads. In the case
of a workqueue-based service, the setup will do something different.

Signed-off-by: Shirley Ma <shirley.ma@oracle.com>
Acked-by: Jeff Layton <jlayton@primarydata.com>
Tested-by: Shirley Ma <shirliey.ma@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

include/linux/sunrpc/svc.h

@@ -61,6 +61,9 @@ struct svc_serv_ops {
 	/* queue up a transport for servicing */
 	void		(*svo_enqueue_xprt)(struct svc_xprt *);
 
+	/* set up thread (or whatever) execution context */
+	int		(*svo_setup)(struct svc_serv *, struct svc_pool *, int);
+
 	/* optional module to count when adding threads (pooled svcs only) */
 	struct module	*svo_module;
 };