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/scsi/aacraid/linit.c

@@ -1540,7 +1540,6 @@ static struct scsi_host_template aac_driver_template = {
 #else
 	.cmd_per_lun			= AAC_NUM_IO_FIB,
 #endif
-	.use_clustering			= ENABLE_CLUSTERING,
 	.emulated			= 1,
 	.no_write_same			= 1,
 };