ceph: additional debugfs output

MDS session state and client global ID is
useful instrumentation when testing.

Signed-off-by: John Spray <john.spray@redhat.com>
diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index f62a098..b82f507 100644
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -95,6 +95,7 @@
 	struct dentry *debugfs_congestion_kb;
 	struct dentry *debugfs_bdi;
 	struct dentry *debugfs_mdsc, *debugfs_mdsmap;
+	struct dentry *debugfs_mds_sessions;
 #endif
 
 #ifdef CONFIG_CEPH_FSCACHE