we have an automation test that adds a vrf named "VRF.TEST":
$ ifquery -a
auto VRF.TEST
iface VRF.TEST
vrf-table auto
$ ifup -a
error: could not determine vlanid
warning: error while writing to file /sys/class/net/VRF.TEST/mtu: [Errno 22] Invalid argument
$
Signed-off-by: Julien Fortin <jfortin@nvidia.com>