tests: Bluetooth: Add regression test to l2cap/stress

43de309b3e72e7784da9557d091a9bd71a46d7dc made a buffer leak.
It was not detected by this test.

Add another configuration, where the final buffer is sent without
fragments in order to exercise the leaky code path.

Signed-off-by: Jonathan Rico <jonathan.rico@nordicsemi.no>
5 files changed