scsi: target: iscsi: Allow AuthMethod=None

Allow negotiating AuthMethod=None at CSG=0 (Security Negotiation) when
authentication is not required. That is required by the CHAP test in
Windows HLK.

Link: https://lore.kernel.org/r/20220718152555.17084-4-d.bogdanov@yadro.com


Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Dmitry Bogdanov <d.bogdanov@yadro.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>