[SCSI] fc_transport: Check portstates before invoking target scan

When a target scan is initiated from sysfs, we should check the
portstate prior to invoke scsi_scan_target().
Otherwise scsi_scan_target() might oops as the rport might already
been removed from the scsi host and the traversal from the rport to
the scsi_host in scsi_scan_target() will fail.
Also the portstate already told us that communication with the target
has failed, so it's quite pointless to try.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Cc: James Smart <James.Smart@Emulex.Com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>