Change of mtu is not handled by reclass. Example interface:
```
        br_ctl:
          enabled: true
          type: bridge
          proto: static
          mtu: 1450
          address: ${_param:single_address}
          gateway: ${_param:ctl_gateway}
          netmask: ${_param:control_network_netmask}
          use_interfaces:
          - ${_param:primary_first_nic}
```