s4: torture: Add an async SMB2_OP_FLUSH + SMB2_OP_CLOSE test to smb2.compound_async.

s4: torture: Add an async SMB2_OP_FLUSH + SMB2_OP_CLOSE test to smb2.compound_async.

Shows we fail sending an SMB2_OP_FLUSH + SMB2_OP_CLOSE
compound. Internally the flush goes async and
we free the req, then we process the close.
When the flush completes it tries to access
already freed data.

Found using the Apple MacOSX client at SNIA SDC 2022.

Add knownfail.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15172

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
(back-ported from commit 17a110c1b58196eb8ecf3c76eb97e8508976c544)