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/bitcomp.c b/src/bitcomp.c
index 94f60eb..d5a9310 100644
--- a/src/bitcomp.c
+++ b/src/bitcomp.c
@@ -1,10 +1,13 @@
 /*! \file bitcomp.c
  * Osmocom bit compression routines */
 /*
- * (C) 2016 sysmocom s.f.m.c. GmbH by Max Suraev <msuraev@sysmocom.de>
+ * (C) 2016 by sysmocom - s.f.m.c. GmbH
+ * Author: Max Suraev <msuraev@sysmocom.de>
  *
  * 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