test/benchmark/ipv4_fwd: Implement an option to use VLANs.
test/benchmark/ipv4_fwd: Implement an option to use VLANs.

Implement option -a to set the number of VLANs to use. Default is
zero, i.e. VLANs are not used.

Signed-off-by: Jere Leppänen <14957520de8d9815e0c353a07fe23c737f0171e9@nokia.com>
Reviewed-by: Valentin Radulescu <5c0267d222138450b4835b40b746ecdf0117cfc8@enea.com>

OpenFastPath/ofp,OpenFastPath/ofp,OpenFastPath/ofp,OpenFastPath/ofp