rte_stats_bitrate_free() has been in DPDK since 20.11.
Its signature is very basic as it just frees an opaque
data struct allocated in rte_stats_bitrate_create()
and returns void.
It's unlikely that such a basic signature would need to change
so might as well promote it to stable for the next major ABI.
Signed-off-by: Kevin Traynor <ktraynor@redhat.com>