Comment 2 for bug 723488

Check if the field "injected" in table "networks" is set to "1". If this field is "0" there will be no network configuration injected into new instances.

Take a look into the nova-compute logfile, you'll find there some logging messages about the injection.

            if key:
                LOG.info(_('instance %(inst_name)s: injecting key into'
                        ' image %(img_id)s') % locals())
            if net:
                LOG.info(_('instance %(inst_name)s: injecting net into'
                        ' image %(img_id)s') % locals())

I don't think that the filterref defintion in your libvirt.xml file has something in common with the DHCPREQUEST. It's only a filter rule for the nwfilter in libvirt (take a look here: http://libvirt.org/formatnwfilter.html).

Try to login through the serial console after spawning the instance and check the network configuration.