Fix license headers: Should have been AGPLv3+, not GPLv2+

I'm not sure why so many files (particularly written by Neels)
did contain a GPLv2+ header, instead of the AGPLv3+ which is the
actual overall project license.  I consider it a mistake.

In any case, any copyrightable contribution to those files was done by
sysmocom employees, so I as managing directory can legally make a
license change, whther or not it was a mistake early on or not.

The only GPLv2-or-later file remaining is mncc_internal.c, as it has
more contributors and a longer history.

Change-Id: I8650697592b3160c4d0a7c61ae9c46d4aacb3bef
diff --git a/src/libmsc/ran_msg_a.c b/src/libmsc/ran_msg_a.c
index 8cf6bfa..d904120 100644
--- a/src/libmsc/ran_msg_a.c
+++ b/src/libmsc/ran_msg_a.c
@@ -5,17 +5,17 @@
  *
  * Author: Neels Hofmeyr
  *
- * SPDX-License-Identifier: GPL-2.0+
+ * SPDX-License-Identifier: AGPL-3.0+
  *
  * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
  * (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
+ * GNU Affero General Public License for more details.
  */
 
 #include <osmocom/core/byteswap.h>