Add major version in Via header

To help track our adoption rate of the new Varnish versions, add the major
version in the default Via header added by us.

bin/varnishd/cache/cache_req_fsm.c

@@ -123,7 +123,7 @@ cnt_deliver(struct worker *wrk, struct req *req)
 	http_PrintfHeader(req->resp, "Age: %.0f",
 	    req->t_resp - req->obj->exp.t_origin);
 
-	http_SetHeader(req->resp, "Via: 1.1 varnish");
+	http_SetHeader(req->resp, "Via: 1.1 varnish (v4)");
 
 	if (cache_param->http_gzip_support && req->obj->gziped &&
 	    !RFC2616_Req_Gzip(req->http))