tc-testing: add test-cases for numeric and invalid control action

Only the police action allows us to specify an arbitrary numeric value
for the control action. This change introduces an explicit test case
for the above feature and then leverage it for testing the kernel behavior
for invalid control actions (reject).

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>