scsi: sd: change allow_restart to bool in sysfs interface

/sys/class/scsi_disk/0:2:0:0/allow_restart can be changed to 0
unexpectedly by writing an invalid string such as the following:

echo asdf > /sys/class/scsi_disk/0:2:0:0/allow_restart

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