app/flow-perf: fix memory leak from RSS action

app/flow-perf: fix memory leak from RSS action

Currently, each call for add_rss_action will allocate
extra memory for rss_data, which will reflect bad results
on memory consumption for all flows, and will leads into
memory leak.

In this fix, it will check if it's allocated before
reallocating it.

Fixes: bf3688f1e816 ("app/flow-perf: add insertion rate calculation")
Cc: stable@dpdk.org
Signed-off-by: Wisam Jaddo <wisamm@mellanox.com>
Acked-by: Alexander Kozyrev <akozyrev@nvidia.com>