ipvlan: play well with macvlan device

If a device is already a macvlan port then refuse to use it as
an ipvlan port in the early stage of port creation.

	thost1:~# ip link add link eth0 mvl0 type macvlan
	thost1:~# echo $?
	0
	thost1:~# ip link add link eth0 ipvl0 type ipvlan
	RTNETLINK answers: Device or resource busy
	thost1:~# echo $?
	2
	thost1:~#
Signed-off-by: Mahesh Bandewar <maheshb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ipvlan/ipvlan_main.c

@@ -38,6 +38,12 @@ static int ipvlan_port_create(struct net_device *dev)
 		netdev_err(dev, "Master is either lo or non-ether device\n");
 		return -EINVAL;
 	}
+
+	if (netif_is_macvlan_port(dev)) {
+		netdev_err(dev, "Master is a macvlan port.\n");
+		return -EBUSY;
+	}
+
 	port = kzalloc(sizeof(struct ipvl_port), GFP_KERNEL);
 	if (!port)
 		return -ENOMEM;