[SCSI] update max sdev block limit

Updated patch to address comments from Pat Mansfield and Michael Reed:
Bumped max to 600 (10mins). Set default dev_loss_tmo to a value other
than the max (30s).

Signed-off-by: James Smart <James.Smart@emulex.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>