QoS Hook
========
libvirt domain xml:
<interface>
    ...
    <bandwidth>
        <inbound average='1' peak='2' burst='5'/>
        <outbound average='0.5'/>
    </bandwidth>
    ...
</interface>

Note:
    for average, peak, and burst explanation look at:
    # man tc tbf

'average' attribute is mandatory,
inbound or outbound elements can be once but not mandatory

syntax:
qos=00:11:22:33:44:55=in{'average':'1','peek':'2','burst':'5'}^out{'average':'1'}&11:11:11:11:11:11=...
    i.e: qos=mac=in{...}^out{...}&mac..
    add QoS to VM interface, can control the in and out traffic by:
    average traffic, peek traffic and burst limit
