net_sched: sch_plug: plug_qdisc_ops is static

net/sched/sch_plug.c:211:18: warning: symbol 'plug_qdisc_ops' was not
declared. Should it be static?
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_plug.c

@@ -208,7 +208,7 @@ static int plug_change(struct Qdisc *sch, struct nlattr *opt)
 	return 0;
 }
 
-struct Qdisc_ops plug_qdisc_ops = {
+static struct Qdisc_ops plug_qdisc_ops __read_mostly = {
 	.id          =       "plug",
 	.priv_size   =       sizeof(struct plug_sched_data),
 	.enqueue     =       plug_enqueue,