Add missing copyright header.

Author: Seppo Takalo

features/cellular/framework/API/CellularNetwork.h

@@ -1,4 +1,10 @@
-/*
+/* Copyright (c) 2017,2018 Arm Limited and affiliates.
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software