ceph: make lease code DN specific

The lease code includes a mask in the CEPH_LOCK_* namespace, but that
namespace is changing, and only one mask (formerly _DN == 1) is used, so
hard code for that value for now.

If we ever extend this code to handle leases over different data types we
can extend it accordingly.

Signed-off-by: Sage Weil <sage@newdream.net>
diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 08413c8..5a88b7b 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -2541,7 +2541,7 @@
 		return;
 	lease = msg->front.iov_base;
 	lease->action = action;
-	lease->mask = cpu_to_le16(CEPH_LOCK_DN);
+	lease->mask = cpu_to_le16(1);
 	lease->ino = cpu_to_le64(ceph_vino(inode).ino);
 	lease->first = lease->last = cpu_to_le64(ceph_vino(inode).snap);
 	lease->seq = cpu_to_le32(seq);
@@ -2571,7 +2571,7 @@
 
 	BUG_ON(inode == NULL);
 	BUG_ON(dentry == NULL);
-	BUG_ON(mask != CEPH_LOCK_DN);
+	BUG_ON(mask == 0);
 
 	/* is dentry lease valid? */
 	spin_lock(&dentry->d_lock);