selftests: mlxsw: Add scale test for tc-police

Query the maximum number of supported policers using devlink-resource
and test that this number can be reached by configuring tc filters with
police action. Test that an error is returned in case the maximum number
is exceeded.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>