gtphub: ares vty and init

From sgsn_vty.c, copy the cfg_grx_ggsn_cmd to add an ares server to the static
sgsn_instance.

This is sort of preliminary. As described in comments, the sgsn_ares functions
should actually be separated from the static sgsn structure. gtphub keeps such
an sgsn structure just for the sgsn_ares functions.

Sponsored-by: On-Waves ehi
diff --git a/openbsc/src/gprs/gtphub.c b/openbsc/src/gprs/gtphub.c
index 8af3ff7..8e16497 100644
--- a/openbsc/src/gprs/gtphub.c
+++ b/openbsc/src/gprs/gtphub.c
@@ -1781,7 +1781,14 @@
 	int rc;
 
 	gtphub_init(hub);
-	gtphub_ares_init(hub);
+
+	/* If a Ctrl plane proxy is configured, ares will never be used. */
+	if (!cfg->ggsn_proxy[GTPH_PLANE_CTRL].addr_str) {
+		if (gtphub_ares_init(hub) != 0) {
+			LOG(LOGL_FATAL, "Failed to initialize ares\n");
+			return -1;
+		}
+	}
 
 	/* TODO set hub->restart_counter from external file. */
 
@@ -1806,7 +1813,6 @@
 		}
 	}
 
-
 	for (plane_idx = 0; plane_idx < GTPH_PLANE_N; plane_idx++) {
 		if (gtphub_make_proxy(hub,
 				      &hub->sgsn_proxy[plane_idx],