[doc] Give files a common structure by placing license first (partial)

Followed by doxyen file and group tags.
This patch is only a first attempt to make provide a clean structure,
many more files require rework, too.

core/net/ip/simple-udp.h

@@ -1,18 +1,3 @@
-/**
- * \addtogroup uip
- * @{
- */
-
-
-/**
- * \defgroup simple-udp
- *
- * The default Contiki UDP API is difficult to use. The simple-udp
- * module provides a significantly simpler API.
- *
- * @{
- */
-
 /*
  * Copyright (c) 2011, Swedish Institute of Computer Science.
  * All rights reserved.
@@ -52,6 +37,21 @@
  *
  */
 
+/**
+ * \addtogroup uip
+ * @{
+ */
+
+
+/**
+ * \defgroup simple-udp
+ *
+ * The default Contiki UDP API is difficult to use. The simple-udp
+ * module provides a significantly simpler API.
+ *
+ * @{
+ */
+
 #ifndef SIMPLE_UDP_H
 #define SIMPLE_UDP_H