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_03_41.h b/include/osmocom/gsm/protocol/gsm_03_41.h
index 40051cd..2e0ad69 100644
--- a/include/osmocom/gsm/protocol/gsm_03_41.h
+++ b/include/osmocom/gsm/protocol/gsm_03_41.h
@@ -1,3 +1,6 @@
+/*! \file gsm_03_41.h
+ * GSM TS 03.41 definitions also TS 23.041. */
+
 #pragma once
 
 #include <stdint.h>
@@ -9,8 +12,6 @@
  #define OSMO_IS_LITTLE_ENDIAN 0
 #endif
 
-/* GSM TS 03.41 definitions also TS 23.041*/
-
 #define GSM341_MAX_PAYLOAD	(GSM412_MSG_LEN-sizeof(struct gsm341_ms_message))
 #define GSM341_MAX_CHARS	(GSM341_MAX_PAYLOAD*8/7)
 #define GSM341_7BIT_PADDING	'\r'