gsup_client.h: fix license header: GPLv2+

gsup_client.c is GPLv2 too, having AGPLv3 in the header file does not
make sense.

Change-Id: I3827a7c70d60137ffc654c1ca53c2652bb3df147
diff --git a/include/osmocom/gsupclient/gsup_client.h b/include/osmocom/gsupclient/gsup_client.h
index 154e3e0..b417ade 100644
--- a/include/osmocom/gsupclient/gsup_client.h
+++ b/include/osmocom/gsupclient/gsup_client.h
@@ -6,18 +6,17 @@
  * Author: Jacob Erlbeck
  *
  * 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
- * along with this program.  If not, see <http://www.gnu.org/licenses/>.
- *
+ * You should have received a copy of the GNU General Public License along
+ * with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 #pragma once