Comment 13 for bug 1737640

Ok, package available in proposed.
  Version table:
 *** 0.12.8~16.04.2 500
        500 http://archive.ubuntu.com/ubuntu xenial-proposed/main amd64 Packages

Confusing result right after the upgrade:
root@04-57:~# ifdown -a; ifup -a
RTNETLINK answers: File exists
Failed to bring up ens3.
root@04-57:~# ifdown ens3
ifdown: interface ens3 not configured

rebooting

Now it works:root@04-57:~# ifdown -a; ifup -a
root@04-57:~#

If this test is acceptable, then consider this verified for xenial.