rtnetlink: Add missing manual netlink notification in dev_change_net_namespaces

rtnetlink: Add missing manual netlink notification in dev_change_net_namespaces

Renato Westphal noticed that since commit 962fdef1f91754231942028d2c63e5875349ce9b
"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: Renato Westphal <renatowestphal@gmail.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>