app/testpmd: print fractional part in CPU cycles

app/testpmd: print fractional part in CPU cycles

Change printing of CPU cycles/packet to include fractional part for
accurateness.

Example:

Without patch:
CPU cycles/packet=14
(total cycles=4899533541 / total RX packets=343031966)

With patch:
CPU cycles/packet=14.28
(total cycles=4899533541 / total RX packets=343031966)

Signed-off-by: Dharmik Thakkar <dharmik.thakkar@arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Reviewed-by: Phil Yang <phil.yang@arm.com>
Acked-by: Bernard Iremonger <bernard.iremonger@intel.com>