app/testpmd: support GENEVE header option length

app/testpmd: support GENEVE header option length

The patch adds the GENEVE rte flow option length support to
command line interpreter. The flow command with GENEVE
option items looks like:

    flow create 0 ingress pattern eth / ipv4 / udp / geneve vni
    is 100 optlen is 2 / end actions drop / end

The option length should be specified in 32-bit words, this
value specifies the all options length in the GENEVE header.

Signed-off-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>
Acked-by: Ori Kam <orika@nvidia.com>