app/flow-perf: add runtime option to use unique data

app/flow-perf: add runtime option to use unique data

Current support for unique data is to compile with config.h
var FIXED_VALUES as 0, and this is only supported on
compilation time, as a result the user may use only single
mode for each compilation.

Starting with this commit the user will have the ability to
use this feature on the fly by using this new option:
--unique-data

Example of unique data usage:
Insert many rules with different encap data for a flows that
have encap action in it.

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