net/sched: act_police: add support for packet-per-second policing

Allow a policer action to enforce a rate-limit based on packets-per-second,
configurable using a packet-per-second rate and burst parameters.

e.g.
tc filter add dev tap1 parent ffff: u32 match \
        u32 0 0 police pkts_rate 3000 pkts_burst 1000

Testing was unable to uncover a performance impact of this change on
existing features.

Signed-off-by: Baowen Zheng <baowen.zheng@corigine.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: Louis Peens <louis.peens@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>