gtp: Add a global region for the gtp library of OpenGGSN

We want to use libosmocore/libosmovty in the GGSN sourcecode
and reserve a global region here.
diff --git a/src/logging.c b/src/logging.c
index f9d789d..a4c3e0e 100644
--- a/src/logging.c
+++ b/src/logging.c
@@ -111,6 +111,11 @@
 		.description = "Control Interface",
 		.enabled = 1, .loglevel = LOGL_NOTICE,
 	},
+	[INT2IDX(DLGTP)] = {
+		.name = "DLGTP",
+		.description = "GPRS GTP library",
+		.enabled = 1, .loglevel = LOGL_NOTICE,
+	},
 };
 
 /*! \brief descriptive string for each log level */