Move global ggsn_list into struct sgsn_instance

Change-Id: I9d4c74476b777a866af2796dd376ed50da7b5d01
diff --git a/src/sgsn/sgsn_vty.c b/src/sgsn/sgsn_vty.c
index 4affa9f..b678f07 100644
--- a/src/sgsn/sgsn_vty.c
+++ b/src/sgsn/sgsn_vty.c
@@ -252,7 +252,7 @@
 	vty_out(vty, " gtp local-ip %s%s",
 		inet_ntoa(g_cfg->gtp_listenaddr.sin_addr), VTY_NEWLINE);
 
-	llist_for_each_entry(gctx, &sgsn_ggsn_ctxts, list) {
+	llist_for_each_entry(gctx, &sgsn->ggsn_list, list) {
 		if (gctx->id == UINT32_MAX)
 			continue;