rtnetlink: Add missing manual netlink notification in dev_change_net_namespaces

Renato Westphal noticed that since commit a2835763
"rtnetlink: handle rtnl_link netlink notifications manually" was merged
we no longer send a netlink message when a networking device is moved
from one network namespace to another.

Fix this by adding the missing manual notification in dev_change_net_namespaces.

Since all network devices that are processed by dev_change_net_namspaces are
in the initialized state the complicated tests that guard the manual
rtmsg_ifinfo calls in rollback_registered and register_netdevice are
unnecessary and we can just perform a plain notification.

Cc: stable@kernel.org
Tested-by: NRenato Westphal <renatowestphal@gmail.com>
Signed-off-by: NEric W. Biederman <ebiederm@xmission.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -6115,6 +6115,7 @@ int dev_change_net_namespace(struct net_device *dev, struct net *net, const char
 	*/
 	call_netdevice_notifiers(NETDEV_UNREGISTER, dev);
 	call_netdevice_notifiers(NETDEV_UNREGISTER_BATCH, dev);
+	rtmsg_ifinfo(RTM_DELLINK, dev, ~0U);
 
 	/*
 	 *	Flush the unicast and multicast chains