Add a service subpackage
    
    This contains a systemd unit, and the logic to be able to save and
    reload functionality on shutdown/startup.
    
    This also adds a missing explicit dependency on the ipset-libs
    subpackage in the base package. It is needed to cover the case where a
    user would update one explicitly (e.g yum update ipset) as they need to
    be kept in sync.