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/gprs_rlc.c b/src/gsm/gprs_rlc.c
index 4b32947..b213b26 100644
--- a/src/gsm/gprs_rlc.c
+++ b/src/gsm/gprs_rlc.c
@@ -1,3 +1,7 @@
+/*! \file gsm/gprs_rlc.c
+ *  helper functions for (E)GPRS RLC according to 3GPP TS 44.060.
+ */
+
 #include <errno.h>
 #include <string.h>
 
@@ -5,10 +9,6 @@
 #include <osmocom/coding/gsm0503_coding.h>
 #include <osmocom/gprs/protocol/gsm_04_60.h>
 
-/*! \file gsm/gprs_rlc.c
- *  helper functions for (E)GPRS RLC according to 3GPP TS 44.060
- */
-
 #define EGPRS_CPS_TYPE1_TBL_SZ		29
 #define EGPRS_CPS_TYPE2_TBL_SZ		8
 #define EGPRS_CPS_TYPE3_TBL_SZ		16