BNG statistics exported on prometheus

The BNG statistics now are single events per attachment, the attributes of the events also changed slightly.
The BNG statistics are also all optional, if not present they won't be pushed on Prometheus.

Change-Id: I361578209b35c7bbbcdd6fd8ec37df07a67eb71b
diff --git a/main.go b/main.go
index 39c4700..752882b 100644
--- a/main.go
+++ b/main.go
@@ -109,15 +109,17 @@
 	prometheus.MustRegister(onosaaaRequestRttMillis)
 	prometheus.MustRegister(onosaaaRequestReTx)
 
-	prometheus.MustRegister(onosPppoeUpTermBytes)
-	prometheus.MustRegister(onosPppoeUpTermPackets)
-	prometheus.MustRegister(onosPppoeUpDropBytes)
-	prometheus.MustRegister(onosPppoeUpDropPackets)
-	prometheus.MustRegister(onosPppoeUpControlPackets)
-	prometheus.MustRegister(onosPppoeDownRxBytes)
-	prometheus.MustRegister(onosPppoeDownRxPackets)
-	prometheus.MustRegister(onosPppoeDownTxBytes)
-	prometheus.MustRegister(onosPppoeDownTxPackets)
+	prometheus.MustRegister(onosBngUpTxBytes)
+	prometheus.MustRegister(onosBngUpTxPackets)
+	prometheus.MustRegister(onosBngUpDropBytes)
+	prometheus.MustRegister(onosBngUpDropPackets)
+	prometheus.MustRegister(onosBngControlPackets)
+	prometheus.MustRegister(onosBngDownRxBytes)
+	prometheus.MustRegister(onosBngDownRxPackets)
+	prometheus.MustRegister(onosBngDownTxBytes)
+	prometheus.MustRegister(onosBngDownTxPackets)
+	prometheus.MustRegister(onosBngDownDropPackets)
+	prometheus.MustRegister(onosBngDownDropBytes)
 
 	prometheus.MustRegister(deviceLaserBiasCurrent)
 	prometheus.MustRegister(deviceTemperature)