app/flow-perf: refactor flows handler

app/flow-perf: refactor flows handler

Provide the flows_handler() function the ability to control
flow performance processes. It is made possible after the
introduction of the insert_flows() function.

Also provide to the flows_handler() function the ability to print
the DPDK layer memory consumption of rte_flow rule, regardless
if deletion feature is enabled or not, while in previous
solution it was printing all memory changes after flows_handler().
Thus if deletion is there, it will not provide any memory that
represents the rte_flow rule size.

Also current design is easier to read and understand.

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