selftests: forwarding: Introduce tc actions tests

Add first part of actions tests. This patch only contains tests of gact
ok/drop/trap and mirred redirect egress.

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>