dev-php/libvirt-php: fixes for libvirt_domain_migrate_to_uri2()

With this fix, libvirt_domain_migrate_to_uri2() works if called like this:
libvirt_domain_migrate_to_uri2($domain, $data['newlibvirt'], null, null, $flags, $data['name'], 0);
Meaning the 2 new params "dconnuri" and "dxml" are NULL.
With this libvirt should to the same as with libvirt_domain_migrate_to_uri().

I did not see it working when dxml param is filled!
Example:
libvirt_domain_migrate_to_uri2($domain, $data['newlibvirt'], null, $this->getXML($data['params']), $flags, $data['name'], 0);
Might be that the xml is malformed, I'll send some sample output to CWI by mail.