net/loopback: add missing license

Add the license to the loopback driver header

Change-Id: I9cb2d93c8de6fe490912684fc3dfb20526be812d
Signed-off-by: Flavio Santes <flavio.santes@intel.com>

net/ip/net_driver_loopback.h

@@ -1,2 +1,25 @@
+/*
+ * Copyright (c) 2016 Intel Corporation
+ *
+ * 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
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+ /**
+  * @brief Register loopback driver
+  *
+  * This routine registers the loopback driver.
+  *
+  * @return always 0
+  */
 
 int net_driver_loopback_init(void);