block: disable I/O stats accounting by default

While Android userspace (e.g. storaged) does use iostats via
/proc/diskstats, init will explicitly enable iostats for the devices on
which it is primarily used - sda and sdf. Avoid the 0.5-1% overhead for
block devices that do not need it.

Signed-off-by: kdrag0n <dragon@khronodragon.com>

include/linux/blkdev.h

@@ -752,13 +752,11 @@ struct request_queue {
 #define QUEUE_FLAG_QUIESCED    28	/* queue has been quiesced */
 #define QUEUE_FLAG_PREEMPT_ONLY 29	/* only process REQ_PREEMPT requests */
 
-#define QUEUE_FLAG_DEFAULT	((1 << QUEUE_FLAG_IO_STAT) |		\
-				 (1 << QUEUE_FLAG_STACKABLE)	|	\
+#define QUEUE_FLAG_DEFAULT	((1 << QUEUE_FLAG_STACKABLE)	|	\
 				 (1 << QUEUE_FLAG_SAME_COMP)	|	\
 				 (1 << QUEUE_FLAG_ADD_RANDOM))
 
-#define QUEUE_FLAG_MQ_DEFAULT	((1 << QUEUE_FLAG_IO_STAT) |		\
-				 (1 << QUEUE_FLAG_STACKABLE)	|	\
+#define QUEUE_FLAG_MQ_DEFAULT	((1 << QUEUE_FLAG_STACKABLE)	|	\
 				 (1 << QUEUE_FLAG_SAME_COMP)	|	\
 				 (1 << QUEUE_FLAG_POLL))