netprio_cgroup: don't allocate prio table when a device is registered

So we delay the allocation till the priority is set through cgroup,
and this makes skb_update_priority() faster when it's not set.

This also eliminates an off-by-one bug similar with the one fixed
in the previous patch.

Origionally-authored-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: "David S. Miller" <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/netprio_cgroup.c

@@ -271,19 +271,13 @@ static int netprio_device_event(struct notifier_block *unused,
 {
 	struct net_device *dev = ptr;
 	struct netprio_map *old;
-	u32 max_len = atomic_read(&max_prioidx);
 
 	/*
 	 * Note this is called with rtnl_lock held so we have update side
 	 * protection on our rcu assignments
 	 */
 
 	switch (event) {
-
-	case NETDEV_REGISTER:
-		if (max_len)
-			extend_netdev_table(dev, max_len);
-		break;
 	case NETDEV_UNREGISTER:
 		old = rtnl_dereference(dev->priomap);
 		RCU_INIT_POINTER(dev->priomap, NULL);