Fixes for avahi package (RELENG_2_1 branch)

Using anything other than "local" for the "domain-name" parameter will prevent service registration from working, as avahi doesn't actually support unicast DNS updates. Also, there should not be any quotes around the contents of the "browse-domains" parameter, as avahi treats these as part of the domain name(s). Finally, the package does start dbus now (and relies on it), so the enable-dbus parameter should be set accordingly.