修改***.xml文件如下：

原来：

    <interface type='bridge'>
      <mac address='00:0c:29:38:ae:6e'/>
      <source bridge='br0'/>
      <model type='rtl8139'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>

修改后：   

<interface type='bridge'>
      <mac address='00:0c:29:ae:5f:df'/>
      <source bridge='br0'/>
      <model type='e1000'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>

【备注】：e1000比rtl8139的网速传输性能更好。