selftests: mlxsw: tc_flower_scale: Add a traffic test

Add a test that checks that the created filters do actually trigger on
matching traffic.

Exercising all the rules would be a very lengthy process. Instead, take a
log2 subset of rules. The logic behind picking log2 rules is that then
every bit of the instantiated item's number is exercised. This should catch
issues whether they happen at the high end, low end, or somewhere in
between.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Amit Cohen <amcohen@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>