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/gprs_rlc.c b/src/gsm/gprs_rlc.c
index d2c05b7..bdfc8ea 100644
--- a/src/gsm/gprs_rlc.c
+++ b/src/gsm/gprs_rlc.c
@@ -1,5 +1,12 @@
 /*! \file gsm/gprs_rlc.c
  *  helper functions for (E)GPRS RLC according to 3GPP TS 44.060.
+ *
+ *  (C) 2016 by Thomas Thou
+ *  (C) 2016-2017 by sysmocom - s.f.m.c. GmbH
+ *  (C) 2017 by Harald Welte <laforge@gnumonks.org>
+ *  All Rights Reserved.
+ *
+ *  SPDX-License-Identifier: GPL-2.0+
  */
 
 #include <errno.h>