ceph: handle session flush message

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
diff --git a/fs/ceph/strings.c b/fs/ceph/strings.c
index 89fa4a9..4440f44 100644
--- a/fs/ceph/strings.c
+++ b/fs/ceph/strings.c
@@ -41,6 +41,8 @@
 	case CEPH_SESSION_RENEWCAPS: return "renewcaps";
 	case CEPH_SESSION_STALE: return "stale";
 	case CEPH_SESSION_RECALL_STATE: return "recall_state";
+	case CEPH_SESSION_FLUSHMSG: return "flushmsg";
+	case CEPH_SESSION_FLUSHMSG_ACK: return "flushmsg_ack";
 	}
 	return "???";
 }