examples/l2fwd-crypto: fix stats refresh rate

examples/l2fwd-crypto: fix stats refresh rate

TIMER_MILLISECOND is defined as the number of cpu cycles per millisecond,
current definition is correct for cores with frequency of 2GHZ, for cores
with different frequency, it caused different periods between refresh,
(i.e. the definition is about 14ms on ARM cores).
The devarg that stated the period between stats print was not used,
instead, it was always defaulted to 10 seconds (on 2GHZ core).

Use DPDK API to get CPU frequency, to define TIMER_MILLISECOND.
Use the refresh period devarg instead of defaulting to 10s always.

Fixes: 387259bd6c67 ("examples/l2fwd-crypto: add sample application")
Cc: stable@dpdk.org
Signed-off-by: Raja Zidane <rzidane@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>
Acked-by: Akhil Goyal <gakhil@marvell.com>