ipvlan: advertise link netns via netlink

Assign rtnl_link_ops->get_link_net() callback so that IFLA_LINK_NETNSID is
added to rtnetlink messages.

Test commands:
    ip netns add nst
    ip link add dummy0 type dummy
    ip link add ipvlan0 link dummy0 type ipvlan
    ip link set ipvlan0 netns nst
    ip netns exec nst ip link show ipvlan0

Result:
    ---Before---
    6: ipvlan0@if5: <BROADCAST,MULTICAST> ...
        link/ether 82:3a:78:ab:60:50 brd ff:ff:ff:ff:ff:ff

    ---After---
    12: ipvlan0@if11: <BROADCAST,MULTICAST> ...
        link/ether 42:b1:ad:57:4e:27 brd ff:ff:ff:ff:ff:ff link-netnsid 0
                                                           ~~~~~~~~~~~~~~
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ipvlan/ipvlan_main.c

@@ -684,6 +684,13 @@ static const struct nla_policy ipvlan_nl_policy[IFLA_IPVLAN_MAX + 1] =
 	[IFLA_IPVLAN_FLAGS] = { .type = NLA_U16 },
 };
 
+static struct net *ipvlan_get_link_net(const struct net_device *dev)
+{
+	struct ipvl_dev *ipvlan = netdev_priv(dev);
+
+	return dev_net(ipvlan->phy_dev);
+}
+
 static struct rtnl_link_ops ipvlan_link_ops = {
 	.kind		= "ipvlan",
 	.priv_size	= sizeof(struct ipvl_dev),
@@ -691,6 +698,7 @@ static struct rtnl_link_ops ipvlan_link_ops = {
 	.setup		= ipvlan_link_setup,
 	.newlink	= ipvlan_link_new,
 	.dellink	= ipvlan_link_delete,
+	.get_link_net   = ipvlan_get_link_net,
 };
 
 int ipvlan_link_register(struct rtnl_link_ops *ops)