TBVOL-3862: Bugfix for DownloadSectionResponse layer serialization

Change-Id: I5dcc0370e88ada914d5a2ded16218ce0155cdc81
diff --git a/messagetypes.go b/messagetypes.go
index 9cbb5a5..6776b06 100644
--- a/messagetypes.go
+++ b/messagetypes.go
@@ -2285,13 +2285,13 @@
 	if err != nil {
 		return err
 	}
-	bytes[0] = omci.SectionNumber
 	if omci.Result > me.DeviceBusy {
 		msg := fmt.Sprintf("invalid results for Download Section response: %v, must be 0..6",
 			omci.Result)
 		return errors.New(msg)
 	}
-	bytes[1] = byte(omci.Result)
+	bytes[0] = byte(omci.Result)
+	bytes[1] = omci.SectionNumber
 	return nil
 }