metric milliseconds computation with golang original method (#11403)

Signed-off-by: Icarus9913 <icaruswu66@qq.com>

metrics/metrics.go

@@ -839,7 +839,7 @@ var GatewayNodeViews = append([]*view.View{
 
 // SinceInMilliseconds returns the duration of time since the provide time as a float64.
 func SinceInMilliseconds(startTime time.Time) float64 {
-	return float64(time.Since(startTime).Nanoseconds()) / 1e6
+	return float64(time.Since(startTime).Milliseconds())
 }
 
 // Timer is a function stopwatch, calling it starts the timer,