Comment 14 for bug 1443607

ok good. So with this patch I think the behavior is the same as nova-network, and is what people expect. The interfaces specified in device_mappings should have their MTUs set by the operating system startup scripts - these will usually be complex devices like bonds with many other parameters.

One last thing, you will need to set network_device_mtu in l3_agent.ini so the other side of the veth (the side in the namespace) gets the correct MTU,