selftests: introduce test for mlxsw tc flower restrictions

Include test of forbidding to have drop rule on mixed-bound
shared block.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>