Add option for controlling buffer scrambling

scramble_buffers bool option, defaults to on.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/fio.h b/fio.h
index e93e8f3..022ba57 100644
--- a/fio.h
+++ b/fio.h
@@ -348,6 +348,7 @@
 	enum fio_fallocate_mode fallocate_mode;
 	unsigned int zero_buffers;
 	unsigned int refill_buffers;
+	unsigned int scramble_buffers;
 	unsigned int time_based;
 	unsigned int disable_lat;
 	unsigned int disable_clat;