ceph: exclude setfilelock requests when calculating oldest tid

setfilelock requests can block for a long time, which can prevent
client from advancing its oldest tid.

Signed-off-by: Yan, Zheng <zyan@redhat.com>
diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
index 294fa23..2ef7999 100644
--- a/fs/ceph/mds_client.h
+++ b/fs/ceph/mds_client.h
@@ -296,6 +296,8 @@
 	spinlock_t              snap_empty_lock;  /* protect snap_empty */
 
 	u64                    last_tid;      /* most recent mds request */
+	u64                    oldest_tid;    /* oldest incomplete mds request,
+						 excluding setfilelock requests */
 	struct rb_root         request_tree;  /* pending mds requests */
 	struct delayed_work    delayed_work;  /* delayed work */
 	unsigned long    last_renew_caps;  /* last time we renewed our caps */