scsi: target: iscs: Make write_pending_must_be_called a bit field

Subsequent commits add more on/off type of settings to the
target_core_fabric_ops struct so this makes write_pending_must_be_called a
bit field instead of a bool to better organize the settings.

Signed-off-by: Mike Christie <michael.christie@oracle.com>
Link: https://lore.kernel.org/r/20230928020907.5730-1-michael.christie@oracle.com


Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>