[GPRS] NS: VTY: Move all local ip/port bind values into 'ns' node

This removes the requirement for gb_proxy and sgsn to have duplicate
vty parsing code
diff --git a/openbsc/src/gprs/gb_proxy_main.c b/openbsc/src/gprs/gb_proxy_main.c
index 1b39a2e..71d6086 100644
--- a/openbsc/src/gprs/gb_proxy_main.c
+++ b/openbsc/src/gprs/gb_proxy_main.c
@@ -238,20 +238,17 @@
 		exit(2);
 	}
 
-	rc = nsip_listen(bssgp_nsi, gbcfg.nsip_listen_ip,
-			 gbcfg.nsip_listen_port);
+	rc = gprs_ns_nsip_listen(bssgp_nsi);
 	if (rc < 0) {
 		LOGP(DGPRS, LOGL_FATAL, "Cannot bind/listen on NSIP socket\n");
 		exit(2);
 	}
 
-	if (gbcfg.frgre_enabled) {
-		rc = gprs_ns_frgre_listen(bssgp_nsi, gbcfg.nsip_listen_ip);
-		if (rc < 0) {
-			LOGP(DGPRS, LOGL_FATAL, "Cannot bind/listen GRE "
-				"socket. Do you have CAP_NET_RAW?\n");
-			exit(2);
-		}
+	rc = gprs_ns_frgre_listen(bssgp_nsi);
+	if (rc < 0) {
+		LOGP(DGPRS, LOGL_FATAL, "Cannot bind/listen GRE "
+			"socket. Do you have CAP_NET_RAW?\n");
+		exit(2);
 	}
 
 	/* Reset all the persistent NS-VCs that we've read from the config */