expose prometheus node port

Change-Id: I05698ee1dc89bca5f5925807a7b66c8ed0a7a375
diff --git a/bess-upf/templates/service-upf.yaml b/bess-upf/templates/service-upf.yaml
index 30d50c8..d364140 100644
--- a/bess-upf/templates/service-upf.yaml
+++ b/bess-upf/templates/service-upf.yaml
@@ -57,4 +57,9 @@
     port: 8000
   - name: prometheus-exporter
     protocol: TCP
-    port: 8080
+    port: {{ .Values.config.upf.prometheus.port }}
+{{- if eq .Values.service.type "NodePort" }}
+{{- if .Values.config.upf.prometheus.nodePort }}
+    nodePort: {{ .Values.config.upf.prometheus.nodePort }}
+{{- end }}
+{{- end }}