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/gsm/gsup.c b/src/gsm/gsup.c
index e5b0a66..eb829f7 100644
--- a/src/gsm/gsup.c
+++ b/src/gsm/gsup.c
@@ -1,10 +1,11 @@
 /*
- * (C) 2014 by sysmocom s.f.m.c. GmbH
+ * (C) 2014 by sysmocom - s.f.m.c. GmbH
+ * Author: Jacob Erlbeck
  * (C) 2015 by Holger Hans Peter Freyther
  * (C) 2016 by Harald Welte <laforge@gnumonks.org>
  * All Rights Reserved
  *
- * Author: Jacob Erlbeck
+ * 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