vlan: fix bond/team enslave of vlan challenged slave/port

In vlan_uses_dev() check for number of vlan devs rather than existence
of vlan_info. The reason is that vlan id 0 is there without appropriate
vlan dev on it by default which prevented from enslaving vlan challenged
dev.

Reported-by: Jon Stanley <[e-mail]>
Signed-off-by: Jiri Pirko <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/bonding/bond_main.c

···
 	/* no need to lock since we're protected by rtnl_lock */
 	if (slave_dev->features & NETIF_F_VLAN_CHALLENGED) {
 		pr_debug("%s: NETIF_F_VLAN_CHALLENGED\n", slave_dev->name);
-		if (bond_vlan_used(bond)) {
+		if (vlan_uses_dev(bond_dev)) {
 			pr_err("%s: Error: cannot enslave VLAN challenged slave %s on VLAN enabled bond %s\n",
 			       bond_dev->name, slave_dev->name, bond_dev->name);
 			return -EPERM;

net/8021q/vlan_core.c

···
 
 bool vlan_uses_dev(const struct net_device *dev)
 {
-	return rtnl_dereference(dev->vlan_info) ? true : false;
+	struct vlan_info *vlan_info;
+
+	ASSERT_RTNL();
+
+	vlan_info = rtnl_dereference(dev->vlan_info);
+	if (!vlan_info)
+		return false;
+	return vlan_info->grp.nr_vlan_devs ? true : false;
 }
 EXPORT_SYMBOL(vlan_uses_dev);