app/flow-perf: export some config as runtime options

app/flow-perf: export some config as runtime options

Some options are needed in the runtime many times, so leaving
it during compilation is not correct. As a result some options
has been exported into command line options to be used at run
time.

The options exported are:
--txq=N
--rxq=N
--txd=N
--rxd=N
--mbuf-size=N
--mbuf-cache-size=N
--total-mbuf-count=N

Signed-off-by: Wisam Jaddo <wisamm@nvidia.com>
Reviewed-by: Alexander Kozyrev <akozyrev@nvidia.com>