render class   | render pkg,         |sysconfig policy   => format+consumer
===============================================================================
[eni]          | [ifupdown]          | [None]            => eni+ifupdown
[eni, netplan] | [ifupdown]          | [None]            => eni+ifupdown
[eni, netplan] | [nplan]             | [None]            => netplan+networkd
[eni, netplan] | [ifupdown]          | [None]            => eni+ifupdown
[eni, netplan] | [ifupdown, netplan] | [None]            => distro.default_render
[eni, netplan] | [ifupdown, netplan] | ["eni, netplan"]  => eni+ifupdown
[eni, netplan] | [ifupdown, netplan] | ["netplan, eni"]  => netplan+networkd


load_available_net_renders
    available = []
    for render in list_of_render_class_names_found_in_source:
        required_pkgs = renderer.required_packages()
        if system_has_packages(required_pkgs):
            available.append(render)
        else:
            log.warning('Net Renderer %s not available, missing req pkg: %s',
                        render, required_pkgs)

    return available

load_distro_net_render_policy()
    policy = config.get('sysconfig.net.render_policy')
    if not policy:
        policy = [distro.default_net_render]
    return policy