Use the right counter for directors index

Fixes	#1060

bin/varnishtest/tests/r01060.vtc

+varnishtest "DNS director tramples on other backends"
+
+server s1 {
+	rxreq
+	txresp
+} -start
+
+server s2 {
+	rxreq
+	txresp
+} -start
+
+varnish v1 -vcl {
+	backend b1 {
+		.host = "${s1_addr}";
+		.port = "${s1_port}";
+	}
+
+	director d1 dns {
+		.list = {
+			.port = "80";
+			"${bad_ip}"/32;
+		}
+		.ttl = 1m;
+	}
+
+	backend b2 {
+		.host = "${s2_addr}";
+		.port = "${s2_port}";
+	}
+
+	sub vcl_recv {
+		set req.backend = d1;
+		if (req.url == "/1") {
+			set req.backend = b1;
+		} else {
+			set req.backend = b2;
+		}
+	}
+} -start
+
+
+client c1 {
+	txreq -url "/1"
+	rxresp
+	txreq -url "/2"
+	rxresp
+} -run

lib/libvcl/vcc_dir_dns.c

@@ -79,7 +79,7 @@ print_backend(struct vcc *tl,
 	AN(vsb);
 	tl->fb = vsb;
 	Fc(tl, 0, "\t{ .host = VGC_backend_%s },\n",vgcname);
-	Fh(tl, 1, "\n#define VGC_backend_%s %d\n", vgcname, serial);
+	Fh(tl, 1, "\n#define VGC_backend_%s %d\n", vgcname, tl->ndirector);
 
 	Fb(tl, 0, "\nstatic const struct vrt_backend vgc_dir_priv_%s = {\n",
 	    vgcname);