create_context_ind(): ignore a non-started default APN

If the default APN has not been started, it is not eligible to be
used in starting of new PDP contexts.

Change-Id: I93b5c205c033f275824ee8bc8cdcf1428fb086df
diff --git a/ggsn/ggsn.c b/ggsn/ggsn.c
index f8aec9d..5852ef6 100644
--- a/ggsn/ggsn.c
+++ b/ggsn/ggsn.c
@@ -451,9 +451,14 @@
 	/* ignore if the APN has not been started */
 	if (!apn->started)
 		apn = NULL;
+
 	/* then try default (if any) */
 	if (!apn)
 		apn = ggsn->cfg.default_apn;
+	/* ignore if the APN has not been started */
+	if (!apn->started)
+		apn = NULL;
+
 	if (!apn) {
 		/* no APN found for what user requested */
 		LOGPPDP(LOGL_NOTICE, pdp, "Unknown APN '%s', rejecting\n", name_buf);