network: Add network bandwidth support to ethernet interfaces
    
    Ethernet interfaces in libvirt currently do not support bandwidth setting.
    For example, following xml file for an interface will not apply these
    settings to corresponding qdiscs.
    
        <interface type="ethernet">
          <mac address="02:36:1d:18:2a:e4"/>
          <model type="virtio"/>
          <script path=""/>
          <target dev="tap361d182a-e4"/>
          <bandwidth>
            <inbound average="984" peak="1024" burst="64"/>
            <outbound average="2000" peak="2048" burst="128"/>
          </bandwidth>
        </interface>
    
    Signed-off-by: Anirban Chakraborty <abchak@juniper.net>
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>