[doc] make sure all SMS related code is part of the 'sms' group

Change-Id: I24c56ccb56d5b39cfb887808f91b715da54c0f8b
diff --git a/src/gsm/gsm0341.c b/src/gsm/gsm0341.c
index 05a0b4a..485023f 100644
--- a/src/gsm/gsm0341.c
+++ b/src/gsm/gsm0341.c
@@ -1,4 +1,3 @@
-/*! \file gsm0341.c */
 /*
  * (C) 2014 by Harald Welte <laforge@gnumonks.org>
  * All Rights Reserved
@@ -30,6 +29,7 @@
 
 /*! \addtogroup sms
  *  @{
+ *  \file gsm0341.c
  */
 
 /*! Encode a 3GPP TS 03.41 SMS-CB message