app/testpmd: support flow aging

app/testpmd: support flow aging

Currently, there is no way to check the aging event or to get the
current aged flows in testpmd, this patch include those implements, it's
included:

- Add new item "flow_aged" to the current print event command arguments.
- Add new command to list all aged flows, meanwhile, we can set
  parameter to destroy it.

Signed-off-by: Dong Zhou <dongz@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>
Acked-by: Ori Kam <orika@mellanox.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>