doxygen: unify use of \file across the board

Considering the various styles and implications found in the sources, edit
scores of files to follow the same API doc guidelines around the doxygen
grouping and the \file tag.

Many files now show a short description in the generated API doc that was so
far only available as C comment.

The guidelines and reasoning behind it is documented at
https://osmocom.org/projects/cellular-infrastructure/wiki/Guidelines_for_API_documentation

In some instances, remove file comments and add to the corresponding group
instead, to be shared among several files (e.g. bitvec).

Change-Id: Ifa70e77e90462b5eb2b0457c70fd25275910c72b
diff --git a/include/osmocom/gsm/protocol/gsm_12_21.h b/include/osmocom/gsm/protocol/gsm_12_21.h
index 1bdee9c..3ef3603 100644
--- a/include/osmocom/gsm/protocol/gsm_12_21.h
+++ b/include/osmocom/gsm/protocol/gsm_12_21.h
@@ -1,9 +1,5 @@
-#pragma once
-
-/* GSM Network Management messages on the A-bis interface 
- * 3GPP TS 12.21 version 8.0.0 Release 1999 / ETSI TS 100 623 V8.0.0 */
-
-/* (C) 2008-2009 by Harald Welte <laforge@gnumonks.org>
+/*
+ * (C) 2008-2009 by Harald Welte <laforge@gnumonks.org>
  * All Rights Reserved
  *
  * This program is free software; you can redistribute it and/or modify
@@ -22,11 +18,11 @@
  *
  */
 
+#pragma once
+
 /*! \addtogroup oml
  *  @{
- */
-
-/*! \file gsm_12_21.h */
+ * \file gsm_12_21.h */
 
 #include <stdint.h>
 #include <stdbool.h>