scsi: flip the default on use_clustering

Most SCSI drivers want to enable "clustering", that is merging of
segments so that they might span more than a single page.  Remove the
ENABLE_CLUSTERING define, and require drivers to explicitly set
DISABLE_CLUSTERING to disable this feature.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/usb/image/microtek.c

@@ -632,7 +632,6 @@ static struct scsi_host_template mts_scsi_host_template = {
 	.sg_tablesize =		SG_ALL,
 	.can_queue =		1,
 	.this_id =		-1,
-	.use_clustering =	1,
 	.emulated =		1,
 	.slave_alloc =		mts_slave_alloc,
 	.slave_configure =	mts_slave_configure,

drivers/usb/storage/scsiglue.c

@@ -639,13 +639,6 @@ static const struct scsi_host_template usb_stor_host_template = {
 	 */
 	.max_sectors =                  240,
 
-	/*
-	 * merge commands... this seems to help performance, but
-	 * periodically someone should test to see which setting is more
-	 * optimal.
-	 */
-	.use_clustering =		1,
-
 	/* emulated HBA */
 	.emulated =			1,