rbd: move stripe_unit and stripe_count into header

This commit added fetching if fancy striping parameters:
    09186ddb rbd: get and check striping parameters

They are almost unused, but the two fields storing the information
really belonged in the rbd_image_header structure.

This patch moves them there.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

drivers/block/rbd.c

@@ -108,6 +108,9 @@ struct rbd_image_header {
 	char *snap_names;
 	u64 *snap_sizes;
 
+	u64 stripe_unit;
+	u64 stripe_count;
+
 	u64 obj_version;
 };
 
@@ -316,9 +319,6 @@ struct rbd_device {
 	u64			parent_overlap;
 	struct rbd_device	*parent;
 
-	u64			stripe_unit;
-	u64			stripe_count;
-
 	/* protects updating the header */
 	struct rw_semaphore     header_rwsem;
 
@@ -3695,8 +3695,8 @@ static int rbd_dev_v2_striping_info(struct rbd_device *rbd_dev)
 				"(got %llu want 1)", stripe_count);
 		return -EINVAL;
 	}
-	rbd_dev->stripe_unit = stripe_unit;
-	rbd_dev->stripe_count = stripe_count;
+	rbd_dev->header.stripe_unit = stripe_unit;
+	rbd_dev->header.stripe_count = stripe_count;
 
 	return 0;
 }