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/src/gsm/lapd_core.c b/src/gsm/lapd_core.c
index 4ad7556..166bf9a 100644
--- a/src/gsm/lapd_core.c
+++ b/src/gsm/lapd_core.c
@@ -1,6 +1,7 @@
-/* LAPD core implementation */
-
-/* (C) 2010-2011 by Harald Welte <laforge@gnumonks.org>
+/*! \file lapd_core.c
+ * LAPD core implementation */
+/*
+ * (C) 2010-2011 by Harald Welte <laforge@gnumonks.org>
  * (C) 2010-2011 by Andreas Eversberg <jolly@eversberg.eu>
  *
  * All Rights Reserved
@@ -23,12 +24,9 @@
 
 /*! \addtogroup lapd
  *  @{
- *  Osmocom LAPD core, used for Q.921, LAPDm and others
- */
-
-/*! \file lapd_core.c */
-
-/*!
+ *
+ * Osmocom LAPD core, used for Q.921, LAPDm and others.
+ *
  * Notes on Buffering: rcv_buffer, tx_queue, tx_hist, send_buffer, send_queue
  *
  * RX data is stored in the rcv_buffer (pointer). If the message is complete, it
@@ -62,6 +60,7 @@
  * will not trigger T200. It will be stoped, when T200 is started in MF EST
  * state. It will also be stoped when leaving MF EST state.
  *
+ * \file lapd_core.c
  */
 
 /* Enable this to test content resolution on network side: