ceph: export ceph_session_state_name function

...so that it can be used from the ceph debugfs
code when dumping session info.

Signed-off-by: John Spray <john.spray@redhat.com>
diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
index 23015f7..3288359 100644
--- a/fs/ceph/mds_client.h
+++ b/fs/ceph/mds_client.h
@@ -330,6 +330,8 @@
 	return s;
 }
 
+extern const char *ceph_session_state_name(int s);
+
 extern void ceph_put_mds_session(struct ceph_mds_session *s);
 
 extern int ceph_send_msg_mds(struct ceph_mds_client *mdsc,