[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/ipv4/uip_arp.h

@@ -1,20 +1,3 @@
-/**
- * \addtogroup uip
- * @{
- */
-
-/**
- * \addtogroup uiparp
- * @{
- */
- 
-/**
- * \file
- * Macros and definitions for the ARP module.
- * \author Adam Dunkels <adam@dunkels.com>
- */
-  
-
 /*
  * Copyright (c) 2001-2003, Adam Dunkels.
  * All rights reserved.
@@ -48,6 +31,22 @@
  *
  */
 
+/**
+ * \file
+ * Macros and definitions for the ARP module.
+ * \author Adam Dunkels <adam@dunkels.com>
+ */
+
+/**
+ * \addtogroup uip
+ * @{
+ */
+
+/**
+ * \addtogroup uiparp
+ * @{
+ */
+ 
 #ifndef UIP_ARP_H_
 #define UIP_ARP_H_