Use voltha-protos version 4.0.2
Bump major version of voltha-lib-go to 4.0.0 as this change results
in incompatible API version compared to previous version

Change-Id: I1def58361fb1d85f07d6948ebf1ffb7a92eb0d4c
diff --git a/pkg/pmmetrics/performance_metrics.go b/pkg/pmmetrics/performance_metrics.go
index 322126b..699e8f0 100644
--- a/pkg/pmmetrics/performance_metrics.go
+++ b/pkg/pmmetrics/performance_metrics.go
@@ -17,7 +17,7 @@
 package pmmetrics
 
 import (
-	"github.com/opencord/voltha-protos/v3/go/voltha"
+	"github.com/opencord/voltha-protos/v4/go/voltha"
 )
 
 // PmMetrics structure holds metric and device info