Rename OpenGGSN to OsmoGGSN

Osmocom has maintained this program since about 7 years now, while
the original author / copyright holder has completely disappeared.

With the introduction of Osmocom-style CTRL and VTY interfaces,
the way how the program is used and configured has substantially
changed.  In order to avoid confusion in terms of configuration file
format etc, let's rename it to OsmoGGSN.

Change-Id: I2da30f7d4828e185bfac1a4e2d8414b01cbe4f9d
diff --git a/AUTHORS b/AUTHORS
index 5f10990..cba1896 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -1,4 +1,4 @@
-OpenGGSN - Gateway GPRS Support Node
+OsmoGGSN - Osmocom Gateway GPRS Support Node, based on OpenGGSN
 Copyright (C) 2002-2004 Mondru AB, Author: Jens Jakobsen <jj@openggsn.org>
 Copyright (C) 2010-2017 Harald Welte <laforge@gnumonks.org>
 Copyright (C) 2012-2016 Holger Hans Peter Freyther <zecke@selfish.org>