app/testpmd: fix burst percentage calculation
app/testpmd: fix burst percentage calculation

The burst % calculation can over flow due to multiplication.
Fix the multiplication and increase the size of variables to
64b.

Fixes: af75078fece3 ("first public release")
Cc: stable@dpdk.org

Signed-off-by: Honnappa Nagarahalli <01ccf438b971cc1d8919c8a7f18443cae9429d8b@arm.com>
Reviewed-by: Phil Yang <5a9b6465c065ff0e1fd5d2cb9eb2185e82f34247@arm.com>
Reviewed-by: Ruifeng Wang <a548d51fbc42485a8ba807711a537e88c2b59dd2@arm.com>
Reviewed-by: Ferruh Yigit <ba8734c3c506d2e3557bd4ac8fdaccd25bdb9aa7@intel.com>
Tested-by: Phil Yang <5a9b6465c065ff0e1fd5d2cb9eb2185e82f34247@arm.com>
Tested-by: Ali Alnubani <cf6d2c19745ffe2f5051227a159da6be2e1adaa2@mellanox.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk