Fix/Update copyright notices; Add SPDX annotation

Let's fix some erroneous/accidential references to wrong license,
update copyright information where applicable and introduce a
SPDX-License-Identifier to all files.

Change-Id: I39af26c6aaaf5c926966391f6565fc5936be21af
diff --git a/src/gb/gprs_ns.c b/src/gb/gprs_ns.c
index a00c8e5..47d170d 100644
--- a/src/gb/gprs_ns.c
+++ b/src/gb/gprs_ns.c
@@ -2,10 +2,13 @@
  * GPRS Networks Service (NS) messages on the Gb interface.
  * 3GPP TS 08.16 version 8.0.1 Release 1999 / ETSI TS 101 299 V8.0.1 (2002-05). */
 /*
- * (C) 2009-2012 by Harald Welte <laforge@gnumonks.org>
+ * (C) 2009-2017 by Harald Welte <laforge@gnumonks.org>
+ * (C) 2016-2017 sysmocom - s.f.m.c. GmbH
  *
  * All Rights Reserved
  *
+ * SPDX-License-Identifier: GPL-2.0+
+ *
  * 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