VOL-3735 Retrieve port counters using the GetExtValue(SingleGetValue) rpc from the openolt adapter

Change-Id: Ie7cd02b6a5b3784d7cc279a616ce88d4ee89ef20
diff --git a/go.mod b/go.mod
index a3bdf52..019debd 100644
--- a/go.mod
+++ b/go.mod
@@ -29,7 +29,7 @@
 	github.com/hashicorp/serf v0.8.4 // indirect
 	github.com/jcmturner/gofork v1.0.0 // indirect
 	github.com/onsi/gomega v1.4.2 // indirect
-	github.com/opencord/voltha-protos/v4 v4.0.6
+	github.com/opencord/voltha-protos/v4 v4.0.8
 	github.com/opentracing/opentracing-go v1.1.0
 	github.com/phayes/freeport v0.0.0-20180830031419-95f893ade6f2
 	github.com/pierrec/lz4 v2.3.0+incompatible // indirect