VMess AEAD based packet length

(cherry picked from commit 08221600082a79376bdc262f2ffec1a3129ae98d)

proxy/vmess/outbound/outbound.go

@@ -119,6 +119,10 @@ func (h *Handler) Process(ctx context.Context, link *transport.Link, dialer inte
 		request.Option.Clear(protocol.RequestOptionChunkMasking)
 	}
 
+	if account.AuthenticatedLengthExperiment {
+		request.Option.Set(protocol.RequestOptionAuthenticatedLength)
+	}
+
 	input := link.Reader
 	output := link.Writer