Fix no PTR records response for cidr ranges (#506)

* set zone for cidr based PTRs

* set zone to request

middleware/kubernetes/handler.go

@@ -26,12 +26,16 @@ func (k Kubernetes) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.M
 	// otherwise delegate to the next in the pipeline.
 	zone := middleware.Zones(k.Zones).Matches(state.Name())
 	if zone == "" {
+		if state.Type() == "PTR" {
 			// If this is a PTR request, and a the request is in a defined
 			// pod/service cidr range, process the request in this middleware,
 			// otherwise pass to next middleware.
-		if state.Type() != "PTR" || !k.IsRequestInReverseRange(state) {
+			if !k.IsRequestInReverseRange(state) {
 				return middleware.NextOrFailure(k.Name(), k.Next, ctx, w, r)
 			}
+			// Set the zone to this specific request.
+			zone = state.Name()
+		}
 	}
 
 	var (