Change license of libosmogb from AGPLv3+ to GPLv2+

The copyright holders Harald Welte, Holger Freyther, Andreas Eversberg
and sysmocom - s.f.m.c. GmbH (represented by Holger and Harald) agree
that the license of libosmogb should be GPLv2+ and not AGPLv3+.

The reason the source files stated AGPLv3+ is due to the history, as
they were moved from OpenBSC to libosmocore at the time we needed to use
them from osmo-pcu.  It was an oversight back then to not re-license
them accordingly.
diff --git a/src/gb/gprs_ns_vty.c b/src/gb/gprs_ns_vty.c
index 4fa60ad..155e1e9 100644
--- a/src/gb/gprs_ns_vty.c
+++ b/src/gb/gprs_ns_vty.c
@@ -5,16 +5,16 @@
  * All Rights Reserved
  *
  * This program is free software; you can redistribute it and/or modify
- * 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
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 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 Affero General Public License for more details.
+ * GNU General Public License for more details.
  *
- * You should have received a copy of the GNU Affero General Public License
+ * You should have received a copy of the GNU General Public License
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  */