net/sched: act_police: use per-cpu counters

use per-CPU counters, instead of sharing a single set of stats with all
cores. This removes the need of using spinlock when statistics are read
or updated.

Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>