net sched: fix kernel leak in act_police

While reviewing commit 1c40be12, I
 audited other users of tc_action_ops->dump for information leaks.

 That commit covered almost all of them but act_police still had a leak.

 opt.limit and opt.capab aren't zeroed out before the structure is
 passed out.

 This patch uses the C99 initializers to zero everything unused out.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Acked-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>