net sched actions police: peg drop stats for conforming traffic

setting conforming action to drop is a valid policy.
When it is set we need to at least see the stats indicating it
for debugging.

Signed-off-by: Roman Mashak <mrv@mojatatu.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>