scsi: core: Allow state transitions from OFFLINE to BLOCKED

When an RSCN gets delayed (or not being sent at all), the transport class
will detect an error, EH kicks in, and eventually will be setting the
device to offline.  If we receive an RSCN after that, the device will
stay in 'offline'.  This patch allows for an 'offline' to 'blocked'
transition, thereby allowing the device to become active again.

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