maas-dhcp needs to quote interface name in /etc/maas/dhcpd.conf

maas dhcp was configured to run on an interface named 'em3.10'.
as a result, I saw errors in /var/log/upstart/maas-dhcp-server.log:

dhcpd self-test failed. Please fix the config file.
The error was:
Internet Systems Consortium DHCP Server 4.2.4
Copyright 2004-2012 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/
/etc/maas/dhcpd.conf line 36: semicolon expected.
       interface em3.
                     ^
/etc/maas/dhcpd.conf line 44: range declaration not allowed here.
       range
        ^
/etc/maas/dhcpd.conf line 49: expecting a declaration
       }
        ^
Configuration file errors encountered -- exiting

The fix is simply that the 'interface' needs to be quoted if it contains a '.' (i suspect any non-alpha numeric char).

Ie, in the snippet here, I hand-quoted 'em3.10'.

subnet 192.168.10.0 netmask 255.255.255.0 {
       if option arch = 00:07 {
          filename "bootx64.efi";
       } else {
          filename "pxelinux.0";
       }
       interface "em3.10";
       ignore-client-uids true;