multi: return parsed types from payload

To separate blinded route parsing from payload parsing, we need to
return the parsed types map so that we can properly validate blinded
data payloads against what we saw in the onion.

htlcswitch/hop/payload_test.go

@@ -479,7 +479,7 @@ func testDecodeHopPayloadValidation(t *testing.T, test decodePayloadTest) {
 		testChildIndex = uint32(9)
 	)
 
-	p, err := hop.NewPayloadFromReader(
+	p, _, err := hop.NewPayloadFromReader(
 		bytes.NewReader(test.payload), test.isFinalHop,
 	)
 	if !reflect.DeepEqual(test.expErr, err) {