KVM: Newer version of libvirt require a namespace to have : in it's name.
A valid configuration for setting MTUs values for virtal interfaces may look
like this now:
<metadata>
<ffho:net xmlns:ffho="https://ffho.net/libvirt/">
<interface name="gw01_v1001">
<mtu size="1610"/>
</interface>
<interface name="gw01_v1205">
<mtu size="1610"/>
</interface>
</ffho:net>
</metadata>
Signed-off-by: Maximilian Wilhelm <max@sdn.clinic>