[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/linkaddr.h

@@ -1,17 +1,3 @@
-/**
- * \addtogroup rime
- * @{
- */
-
-/**
- * \defgroup linkaddr Rime addresses
- * @{
- *
- * The linkaddr module is an abstract representation of addresses in
- * Rime.
- *
- */
-
 /*
  * Copyright (c) 2007, Swedish Institute of Computer Science.
  * All rights reserved.
@@ -51,6 +37,20 @@
  *         Adam Dunkels <adam@sics.se>
  */
 
+/**
+ * \addtogroup rime
+ * @{
+ */
+
+/**
+ * \defgroup linkaddr Rime addresses
+ * @{
+ *
+ * The linkaddr module is an abstract representation of addresses in
+ * Rime.
+ *
+ */
+
 #ifndef LINKADDR_H_
 #define LINKADDR_H_