ipvlan: handle NETDEV_DOWN event

In case of stacked devices, to help propagate the down
link state from the parent/root device (to this leaf device),
handle NETDEV_DOWN event like it is done now for NETDEV_UP.

In the below example, ens5 is the host interface which is the
parent of the ipvlan interface eth0 in the container.

Host:

[root@gkn-podman-x64 ~]# ip link set ens5 down
[root@gkn-podman-x64 ~]# ip -d link show dev ens5
3: ens5: <BROADCAST,MULTICAST> mtu 9000 qdisc mq state DOWN
      ...
[root@gkn-podman-x64 ~]#

Container:

[root@testnode-ol8 /]# ip -d link show dev eth0
2: eth0@if3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9000 state UNKNOWN
        ...
    ipvlan mode l2 bridge
        ...
[root@testnode-ol8 /]#

eth0's state continues to show up as UP even though ens5 is now DOWN.

For macvlan the handling of NETDEV_DOWN event was added in
commit 80fd2d6c ("macvlan: Change status when lower device goes down").
Reported-by: Gia-Khanh Nguyen <gia-khanh.nguyen@oracle.com>
Signed-off-by: Venkat Venkatsubra <venkat.x.venkatsubra@oracle.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ipvlan/ipvlan_main.c

@@ -735,6 +735,7 @@ static int ipvlan_device_event(struct notifier_block *unused,
 
 	switch (event) {
 	case NETDEV_UP:
+	case NETDEV_DOWN:
 	case NETDEV_CHANGE:
 		list_for_each_entry(ipvlan, &port->ipvlans, pnode)
 			netif_stacked_transfer_operstate(ipvlan->phy_dev,