Comment 1 for bug 1102983

This is possible in Icehouse by setting one or more of the following in user.yaml:

neutron::agents::l3::network_device_mtu: 9000
neutron::agents::ovs::veth_mtu: 9000

Refer to:
https://github.com/CiscoSystems/puppet-neutron/blob/icehouse/manifests/agents/l3.pp#L70-L72
https://github.com/CiscoSystems/puppet-neutron/blob/icehouse/manifests/agents/ovs.pp#L31

The MTU's of physical interfaces (e.g. things Neutron uses but doesn't control) would need to be dealt with elsewhere though.