scsi: target: Perform ALUA group changes in one step

scsi: target: Perform ALUA group changes in one step

When userspace changes the LUN's ALUA group, it will set the LUN's group to
NULL then to the new group. Before the new group is set,
target_alua_state_check() will return 0 and allow the I/O to execute. This
has us skip the NULL stage, and just swap in the new group.

Link: https://lore.kernel.org/r/20210930020422.92578-6-michael.christie@oracle.com
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>