selftests: forwarding: fix "ok" action test

Fix the "ok" action test so it checks that packet that is okayed does not
continue to be processed by other rules. Fix error message as well.

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