VOL-1643 Update voltha-lib-go to use voltha-protos v3.0.0

and bump up the version to 3.0.0. voltha-protos is modified to be
compatible with the java language proto compilation. It's a major
change and a major version change has been made.

Change-Id: Ifb93430567ddf96aaa0fbf6e5853aad9e1070f6f
diff --git a/pkg/adapters/common/performance_metrics.go b/pkg/adapters/common/performance_metrics.go
index bcb45f8..7697c05 100644
--- a/pkg/adapters/common/performance_metrics.go
+++ b/pkg/adapters/common/performance_metrics.go
@@ -17,7 +17,7 @@
 package common
 
 import (
-	"github.com/opencord/voltha-protos/v2/go/voltha"
+	"github.com/opencord/voltha-protos/v3/go/voltha"
 )
 
 type PmMetrics struct {