scsi: target: iscsi: Do not require target authentication

scsi: target: iscsi: Do not require target authentication

RFC7143 states that Initiator decides what type of authentication to
use:

The initiator MUST continue with:
    CHAP_N=<N> CHAP_R=<R>
or, if it requires target authentication, with:
    CHAP_N=<N> CHAP_R=<R> CHAP_I=<I> CHAP_C=<C>

Allow one way authentication if mutual authentication is configured.  That
passes some tests from Windows HLK for Mutual CHAP with iSNS.

Link: https://lore.kernel.org/r/20220718152555.17084-5-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>