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_ares.c b/openbsc/src/gprs/gtphub_ares.c
index 8522556..7688b47 100644
--- a/openbsc/src/gprs/gtphub_ares.c
+++ b/openbsc/src/gprs/gtphub_ares.c
@@ -197,7 +197,7 @@
 			LOGP(DGTPHUB, LOGL_DEBUG,
 			     "GGSN resolved from cache: %s -> %s\n",
 			     lookup->apn_oi_str,
-			     gtphub_peer_str(resolved->peer));
+			     gtphub_port_str(resolved->peer));
 			return resolved->peer;
 		}
 	}