VOL-3588 Update OFAgent to support new version of protos

Change-Id: Ic3944779f9a600ebcd5d7a916616f473059e311e
diff --git a/internal/pkg/holder/holder.go b/internal/pkg/holder/holder.go
index 0074582..60b0785 100644
--- a/internal/pkg/holder/holder.go
+++ b/internal/pkg/holder/holder.go
@@ -19,7 +19,7 @@
 import (
 	"sync"
 
-	"github.com/opencord/voltha-protos/v3/go/voltha"
+	"github.com/opencord/voltha-protos/v4/go/voltha"
 )
 
 // VolthaServiceClientHolder provides a consistent (voluntarily unmutable) reference