vlan: add helper which can be called to see if device is used by vlan

also, remove unused vlan_info definition from header

CC: Patrick McHardy <kaber@trash.net>
Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/8021q/vlan_core.c b/net/8021q/vlan_core.c
index 8ca533c..b258da8 100644
--- a/net/8021q/vlan_core.c
+++ b/net/8021q/vlan_core.c
@@ -368,3 +368,9 @@
 		vlan_vid_del(dev, vid_info->vid);
 }
 EXPORT_SYMBOL(vlan_vids_del_by_dev);
+
+bool vlan_uses_dev(const struct net_device *dev)
+{
+	return rtnl_dereference(dev->vlan_info) ? true : false;
+}
+EXPORT_SYMBOL(vlan_uses_dev);