[VOL-4290] Voltha go library updates for gRPC migration

Change-Id: I1aa2774beb6b7ed7419bc45aeb53fcae8a8ecda0
diff --git a/vendor/github.com/opentracing/opentracing-go/noop.go b/vendor/github.com/opentracing/opentracing-go/noop.go
index 0d32f69..f9b680a 100644
--- a/vendor/github.com/opentracing/opentracing-go/noop.go
+++ b/vendor/github.com/opentracing/opentracing-go/noop.go
@@ -21,9 +21,9 @@
 type noopSpanContext struct{}
 
 var (
-	defaultNoopSpanContext = noopSpanContext{}
-	defaultNoopSpan        = noopSpan{}
-	defaultNoopTracer      = NoopTracer{}
+	defaultNoopSpanContext SpanContext = noopSpanContext{}
+	defaultNoopSpan        Span        = noopSpan{}
+	defaultNoopTracer      Tracer      = NoopTracer{}
 )
 
 const (
@@ -35,7 +35,7 @@
 
 // noopSpan:
 func (n noopSpan) Context() SpanContext                                  { return defaultNoopSpanContext }
-func (n noopSpan) SetBaggageItem(key, val string) Span                   { return defaultNoopSpan }
+func (n noopSpan) SetBaggageItem(key, val string) Span                   { return n }
 func (n noopSpan) BaggageItem(key string) string                         { return emptyString }
 func (n noopSpan) SetTag(key string, value interface{}) Span             { return n }
 func (n noopSpan) LogFields(fields ...log.Field)                         {}