block: copy NOMERGE flag from bio to request

bio might have NOMERGE flag set, for example blk_queue_split sets it.
When we initiate request, copy this flag too.
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

include/linux/blk_types.h

@@ -208,7 +208,7 @@ enum rq_flag_bits {
 #define REQ_COMMON_MASK \
 	(REQ_WRITE | REQ_FAILFAST_MASK | REQ_SYNC | REQ_META | REQ_PRIO | \
 	 REQ_DISCARD | REQ_WRITE_SAME | REQ_NOIDLE | REQ_FLUSH | REQ_FUA | \
-	 REQ_SECURE | REQ_INTEGRITY)
+	 REQ_SECURE | REQ_INTEGRITY | REQ_NOMERGE)
 #define REQ_CLONE_MASK		REQ_COMMON_MASK
 
 #define BIO_NO_ADVANCE_ITER_MASK	(REQ_DISCARD|REQ_WRITE_SAME)