app/flow-perf: simplify objects initialization

app/flow-perf: simplify objects initialization

Since items are static then the default values will be zero,
thus the memset to zero value is just a redundant code.

Also remove the all not needed variables, that can be replaced
with direct set to the structure itself.

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