zpay32: update spec test vectors, write features last

This commit updates the BOLT11 test vectors to use the updated versions
from the spec (with TLV bit set). This also pointed out that the
ordering was inconsistent with the spec, in that the payment secret
should be serialized before the feature vector.

zpay32/invoice.go

@@ -1094,6 +1094,14 @@ func writeTaggedFields(bufferBase32 *bytes.Buffer, invoice *Invoice) error {
 			return err
 		}
 	}
+	if invoice.PaymentAddr != nil {
+		err := writeBytes32(
+			bufferBase32, fieldTypeS, *invoice.PaymentAddr,
+		)
+		if err != nil {
+			return err
+		}
+	}
 	if invoice.Features.SerializeSize32() > 0 {
 		var b bytes.Buffer
 		err := invoice.Features.RawFeatureVector.EncodeBase32(&b)
@@ -1106,14 +1114,6 @@ func writeTaggedFields(bufferBase32 *bytes.Buffer, invoice *Invoice) error {
 			return err
 		}
 	}
-	if invoice.PaymentAddr != nil {
-		err := writeBytes32(
-			bufferBase32, fieldTypeS, *invoice.PaymentAddr,
-		)
-		if err != nil {
-			return err
-		}
-	}
 
 	return nil
 }