Change license from ONF-Member-Only to Apache-2.0

Change-Id: If5c78f555fb737a18a3ae4c216ea3e2630b101bc
diff --git a/advanced/upf.rst b/advanced/upf.rst
index 265bad4..a7ddb2b 100644
--- a/advanced/upf.rst
+++ b/advanced/upf.rst
@@ -1,3 +1,6 @@
+.. SPDX-FileCopyrightText: 2021 Open Networking Foundation <info@opennetworking.org>
+.. SPDX-License-Identifier: Apache-2.0
+
 .. _p4_upf:
 
 P4-based User Plane Function (P4-UPF)