vlan: Use is_vlan_dev()

Use simplified is_vlan_dev function.

Signed-off-by: Joonwoo Park <joonwpark81@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/8021q/vlanproc.c b/net/8021q/vlanproc.c
index 08b54b59..6073a88 100644
--- a/net/8021q/vlanproc.c
+++ b/net/8021q/vlanproc.c
@@ -290,7 +290,7 @@
 	static const char fmt[] = "%30s %12lu\n";
 	int i;
 
-	if (!(vlandev->priv_flags & IFF_802_1Q_VLAN))
+	if (!is_vlan_dev(vlandev))
 		return 0;
 
 	seq_printf(seq,