net: sched: make newly activated qdiscs visible

In their .attach callback, mq[prio] only add the qdiscs of the currently
active TX queues to the device's qdisc hash list.
If a user later increases the number of active TX queues, their qdiscs
are not visible via eg. 'tc qdisc show'.

Add a hook to netif_set_real_num_tx_queues() that walks all active
TX queues and adds those which are missing to the hash list.

CC: Eric Dumazet <edumazet@google.com>
CC: Jamal Hadi Salim <jhs@mojatatu.com>
CC: Cong Wang <xiyou.wangcong@gmail.com>
CC: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_generic.c

@@ -1268,6 +1268,27 @@ int dev_qdisc_change_tx_queue_len(struct net_device *dev)
 	return ret;
 }
 
+void dev_qdisc_set_real_num_tx_queues(struct net_device *dev)
+{
+#ifdef CONFIG_NET_SCHED
+	struct Qdisc *sch = dev->qdisc;
+	unsigned int ntx;
+
+	if (!sch)
+		return;
+
+	ASSERT_RTNL();
+
+	for (ntx = 0; ntx < dev->real_num_tx_queues; ntx++) {
+		struct netdev_queue *dev_queue = netdev_get_tx_queue(dev, ntx);
+		struct Qdisc *qdisc = dev_queue->qdisc;
+
+		if (qdisc && !qdisc_hashed(qdisc))
+			qdisc_hash_add(qdisc, false);
+	}
+#endif
+}
+
 static void dev_init_scheduler_queue(struct net_device *dev,
 				     struct netdev_queue *dev_queue,
 				     void *_qdisc)