Code review comment for ~ddstreet/maas:lp1896684

Thanks for finding and fixing this!

This seems to fix the bug for static IP address, have you tested DHCP? Looking at the code[1] I think its correct but it would be good to verify. Couple of other things

1. This needs commit message to land. It should start with "LP: #1896684 - "
2. Unit tests need to be added to ensure we don't regress this.
3. One comment inline below.

[1] https://git.launchpad.net/maas/tree/src/maasserver/dhcp.py#n420