If user enables VLAN support, then the sample application will
create two extra VLAN network interfaces for testing purposes.
The application can be compiled like this for VLAN support:
cmake -DBOARD=qemu_x86 -DOVERLAY_CONFIG=overlay-vlan.conf ..
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>