Comment 0 for bug 1717404

Prior to the switch to nplan, systems (in my case containers) would DHCP for IPv4 and let the kernel do IPv6 auto-configuration whenever a router advertisement comes in.

That's the exact same behavior we see on every single other Linux distribution, but ever since the switch to nplan by default in Ubuntu, we're not getting an IPv6 address anymore when a RA reaches the container.

This was spotted by a new Jenkins test we're running which ensures that every single image we have for LXD will start and get a working IPv4 (through DHCP) and IPv6 address (through RA).

```
PASS: alpine-33-priv has working IPv4 and IPv6 connectivty
PASS: alpine-33-unpriv has working IPv4 and IPv6 connectivty
PASS: alpine-34-priv has working IPv4 and IPv6 connectivty
PASS: alpine-34-unpriv has working IPv4 and IPv6 connectivty
PASS: alpine-35-priv has working IPv4 and IPv6 connectivty
PASS: alpine-35-unpriv has working IPv4 and IPv6 connectivty
PASS: alpine-36-priv has working IPv4 and IPv6 connectivty
PASS: alpine-36-unpriv has working IPv4 and IPv6 connectivty
PASS: alpine-edge-priv has working IPv4 and IPv6 connectivty
PASS: alpine-edge-unpriv has working IPv4 and IPv6 connectivty
PASS: archlinux-priv has working IPv4 and IPv6 connectivty
PASS: archlinux-unpriv has working IPv4 and IPv6 connectivty
PASS: centos-6-priv has working IPv4 and IPv6 connectivty
PASS: centos-6-unpriv has working IPv4 and IPv6 connectivty
PASS: centos-7-priv has working IPv4 and IPv6 connectivty
PASS: centos-7-unpriv has working IPv4 and IPv6 connectivty
PASS: debian-buster-priv has working IPv4 and IPv6 connectivty
PASS: debian-buster-unpriv has working IPv4 and IPv6 connectivty
PASS: debian-jessie-priv has working IPv4 and IPv6 connectivty
PASS: debian-jessie-unpriv has working IPv4 and IPv6 connectivty
PASS: debian-sid-priv has working IPv4 and IPv6 connectivty
PASS: debian-sid-unpriv has working IPv4 and IPv6 connectivty
PASS: debian-stretch-priv has working IPv4 and IPv6 connectivty
PASS: debian-stretch-unpriv has working IPv4 and IPv6 connectivty
PASS: debian-wheezy-priv has working IPv4 and IPv6 connectivty
PASS: debian-wheezy-unpriv has working IPv4 and IPv6 connectivty
PASS: fedora-24-priv has working IPv4 and IPv6 connectivty
PASS: fedora-24-unpriv has working IPv4 and IPv6 connectivty
PASS: fedora-25-priv has working IPv4 and IPv6 connectivty
PASS: fedora-25-unpriv has working IPv4 and IPv6 connectivty
PASS: fedora-26-priv has working IPv4 and IPv6 connectivty
PASS: fedora-26-unpriv has working IPv4 and IPv6 connectivty
PASS: gentoo-priv has working IPv4 and IPv6 connectivty
PASS: gentoo-unpriv has working IPv4 and IPv6 connectivty
PASS: opensuse-422-priv has working IPv4 and IPv6 connectivty
PASS: opensuse-422-unpriv has working IPv4 and IPv6 connectivty
PASS: opensuse-423-priv has working IPv4 and IPv6 connectivty
PASS: opensuse-423-unpriv has working IPv4 and IPv6 connectivty
PASS: oracle-6-priv has working IPv4 and IPv6 connectivty
PASS: oracle-6-unpriv has working IPv4 and IPv6 connectivty
PASS: oracle-7-priv has working IPv4 and IPv6 connectivty
PASS: oracle-7-unpriv has working IPv4 and IPv6 connectivty
PASS: plamo-5x-priv has working IPv4 and IPv6 connectivty
PASS: plamo-5x-unpriv has working IPv4 and IPv6 connectivty
PASS: plamo-6x-priv has working IPv4 and IPv6 connectivty
PASS: plamo-6x-unpriv has working IPv4 and IPv6 connectivty
PASS: sabayon-priv has working IPv4 and IPv6 connectivty
PASS: sabayon-unpriv has working IPv4 and IPv6 connectivty
FAIL: ubuntu-artful-priv doesn't have an IPv6 address
FAIL: ubuntu-artful-unpriv doesn't have an IPv6 address
PASS: ubuntu-core-16-priv has working IPv4 and IPv6 connectivty
PASS: ubuntu-core-16-unpriv has working IPv4 and IPv6 connectivty
PASS: ubuntu-precise-priv has working IPv4 and IPv6 connectivty
PASS: ubuntu-precise-unpriv has working IPv4 and IPv6 connectivty
PASS: ubuntu-trusty-priv has working IPv4 and IPv6 connectivty
PASS: ubuntu-trusty-unpriv has working IPv4 and IPv6 connectivty
PASS: ubuntu-xenial-priv has working IPv4 and IPv6 connectivty
PASS: ubuntu-xenial-unpriv has working IPv4 and IPv6 connectivty
PASS: ubuntu-zesty-priv has working IPv4 and IPv6 connectivty
PASS: ubuntu-zesty-unpriv has working IPv4 and IPv6 connectivty

Test failed
```