drbd: Fixed processing of disk-barrier, disk-flushes and disk-drain

Since drbd_bump_write_ordering() is called in the attaching
process while the disk state is D_ATTACHING, it was not
considering these three flags during attach.

A call to this function was missing form drbd_adm_disk_opts().

Fixed both issues.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
index c5aa084..ce9f4ca 100644
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -1229,6 +1229,9 @@
 	}
 
 	mutex_unlock(&mdev->tconn->conf_update);
+
+	drbd_bump_write_ordering(mdev->tconn, WO_bdev_flush);
+
 	drbd_md_sync(mdev);
 
 	if (mdev->state.conn >= C_CONNECTED)