lnwire: if unable to parse encapsulated error, log length and raw bytes

In this commit, we add additional detail in the error return hen were’e
unable to properly decode an encapsulated error. This additional
logging was added with the goal of being able to track down a lingering
bug, where at times lnd cannot decode a TemporaryChannelFailure
message.

lnwire/onion_error.go

@@ -532,6 +532,7 @@ func (f *FailTemporaryChannelFailure) Decode(r io.Reader, pver uint32) error {
 		f.Update = &ChannelUpdate{}
 		return f.Update.Decode(r, pver)
 	}
+
 	return nil
 }
 
@@ -1031,7 +1032,8 @@ func DecodeFailure(r io.Reader, pver uint32) (FailureMessage, error) {
 	case Serializable:
 		if err := f.Decode(dataReader, pver); err != nil {
 			return nil, fmt.Errorf("unable to decode error "+
-				"update (%T): %v", err, failure)
+				"update (type=%T, len_bytes=%v, bytes=%x): %v",
+				failure, failureLength, failureData[:], err)
 		}
 	}