drbd: Introduced tconn->cstate_mutex

In compatibility mode with old DRBDs, use that as the state_mutex
as well.

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 eeb284a..3d8e631 100644
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -320,7 +320,7 @@
 	if (new_role == R_PRIMARY)
 		request_ping(mdev->tconn); /* Detect a dead peer ASAP */
 
-	mutex_lock(&mdev->state_mutex);
+	mutex_lock(mdev->state_mutex);
 
 	mask.i = 0; mask.role = R_MASK;
 	val.i  = 0; val.role  = new_role;
@@ -439,7 +439,7 @@
 
 	kobject_uevent(&disk_to_dev(mdev->vdisk)->kobj, KOBJ_CHANGE);
  fail:
-	mutex_unlock(&mdev->state_mutex);
+	mutex_unlock(mdev->state_mutex);
 	return rv;
 }
 
@@ -2162,7 +2162,7 @@
 		return 0;
 	}
 
-	mutex_lock(&mdev->state_mutex); /* Protects us against serialized state changes. */
+	mutex_lock(mdev->state_mutex); /* Protects us against serialized state changes. */
 
 	if (!get_ldev(mdev)) {
 		retcode = ERR_NO_DISK;
@@ -2204,7 +2204,7 @@
 out_dec:
 	put_ldev(mdev);
 out:
-	mutex_unlock(&mdev->state_mutex);
+	mutex_unlock(mdev->state_mutex);
 
 	reply->ret_code = retcode;
 	return 0;