Move global ggsn_list into struct sgsn_instance

Change-Id: I9d4c74476b777a866af2796dd376ed50da7b5d01
diff --git a/src/sgsn/gtp_ggsn.c b/src/sgsn/gtp_ggsn.c
index 0a670e1..f8e09e8 100644
--- a/src/sgsn/gtp_ggsn.c
+++ b/src/sgsn/gtp_ggsn.c
@@ -73,7 +73,7 @@
 	ggc->gsn = sgsn->gsn;
 	INIT_LLIST_HEAD(&ggc->pdp_list);
 	osmo_timer_setup(&ggc->echo_timer, echo_timer_cb, ggc);
-	llist_add(&ggc->list, &sgsn_ggsn_ctxts);
+	llist_add(&ggc->list, &sgsn->ggsn_list);
 
 	return ggc;
 }
@@ -89,7 +89,7 @@
 {
 	struct sgsn_ggsn_ctx *ggc;
 
-	llist_for_each_entry(ggc, &sgsn_ggsn_ctxts, list) {
+	llist_for_each_entry(ggc, &sgsn->ggsn_list, list) {
 		if (id == ggc->id)
 			return ggc;
 	}
@@ -100,7 +100,7 @@
 {
 	struct sgsn_ggsn_ctx *ggc;
 
-	llist_for_each_entry(ggc, &sgsn_ggsn_ctxts, list) {
+	llist_for_each_entry(ggc, &sgsn->ggsn_list, list) {
 		if (!memcmp(addr, &ggc->remote_addr, sizeof(*addr)))
 			return ggc;
 	}