Tidy up \file & \author blocks under core/net/ipv6

* Make these blocks appear in the respective module pages
* Re-word \file blocks to bring them up to speed with what each file actually does nowadays

core/net/ipv6/uip-ds6-nbr.c

@@ -29,20 +29,20 @@
  *
  */
 
+/**
+ * \addtogroup uip6
+ * @{
+ */
+
 /**
  * \file
- *         IPv6 Neighbor cache (link-layer/IPv6 address mapping)
+ *    IPv6 Neighbor cache (link-layer/IPv6 address mapping)
  * \author Mathilde Durvy <mdurvy@cisco.com>
  * \author Julien Abeille <jabeille@cisco.com>
  * \author Simon Duquennoy <simonduq@sics.se>
  *
  */
 
-/**
- * \addtogroup uip6
- * @{
- */
-
 #include <string.h>
 #include <stdlib.h>
 #include <stddef.h>