bitrate: fix integer roundoff
bitrate: fix integer roundoff

In the absence of traffic, it is possible for the bitrate moving average
to get stuck at a non-zero value, due to the calculated delta being less
than what an integer can represent.

Fixes: 2ad7ba9a6567 ("bitrate: add bitrate statistics library")

Signed-off-by: Remy Horton <34c343e92f0e27f7a8e26a1d8d2146ae7c7dd1a3@intel.com>

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