selftests: forwarding: fix flags passed to first drop rule in gact_drop_and_ok_test

Fix copy&paste error and pass proper flags.

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