[SCSI] seperate max_sectors from max_hw_sectors

- export __blk_put_request and blk_execute_rq_nowait
needed for async REQ_BLOCK_PC requests
- seperate max_hw_sectors and max_sectors for block/scsi_ioctl.c and
SG_IO bio.c helpers per Jens's last comments. Since block/scsi_ioctl.c SG_IO was
already testing against max_sectors and SCSI-ml was setting max_sectors and
max_hw_sectors to the same value this does not change any scsi SG_IO behavior. It only
prepares ll_rw_blk.c, scsi_ioctl.c and bio.c for when SCSI-ml begins to set
a valid max_hw_sectors for all LLDs. Today if a LLD does not set it
SCSI-ml sets it to a safe default and some LLDs set it to a artificial low
value to overcome memory and feedback issues.

Note: Since we now cap max_sectors to BLK_DEF_MAX_SECTORS, which is 1024,
drivers that used to call blk_queue_max_sectors with a large value of
max_sectors will now see the fs requests capped to BLK_DEF_MAX_SECTORS.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>
diff --git a/block/scsi_ioctl.c b/block/scsi_ioctl.c
index 382dea7..4e390df 100644
--- a/block/scsi_ioctl.c
+++ b/block/scsi_ioctl.c
@@ -233,7 +233,7 @@
 	if (verify_command(file, cmd))
 		return -EPERM;
 
-	if (hdr->dxfer_len > (q->max_sectors << 9))
+	if (hdr->dxfer_len > (q->max_hw_sectors << 9))
 		return -EIO;
 
 	if (hdr->dxfer_len)