network_conf: Introduce virNetworkObjEndAPI
    
    This is practically copy of qemuDomObjEndAPI. The reason why is
    it so widely available is to avoid code duplication, since the
    function is going to be called from our bridge driver, test
    driver and parallels driver too.
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>