selftests: forwarding: Add tc-police tests for packets per second

Test tc-police action for packets per second.
The test is mainly in scenarios Rx policing and Tx policing.
The test passes with veth pairs ports.

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