htlcswitch: ensure onion related errors always have the BadOnion bit set

In this commit, we fix a lingering protocol level bug when reporting
errors encountered during onion blob processing. The spec states that
if one sends an UpdateFailMalformedHtlc, then the error reason MUST
have the BadOnion bit set. Before this commit, we would return
CodeTemporaryChannelFailure. This is incorrect as this doesn’t have the
BadOnio bit set.

htlcswitch/iterator.go

@@ -170,7 +170,7 @@ func (p *OnionProcessor) DecodeHopIterator(r io.Reader, rHash []byte) (HopIterat
 			return nil, lnwire.CodeInvalidOnionKey
 		default:
 			log.Errorf("unable to decode onion packet: %v", err)
-			return nil, lnwire.CodeTemporaryChannelFailure
+			return nil, lnwire.CodeInvalidOnionKey
 		}
 	}
 
@@ -190,7 +190,7 @@ func (p *OnionProcessor) DecodeHopIterator(r io.Reader, rHash []byte) (HopIterat
 			return nil, lnwire.CodeInvalidOnionKey
 		default:
 			log.Errorf("unable to process onion packet: %v", err)
-			return nil, lnwire.CodeTemporaryChannelFailure
+			return nil, lnwire.CodeInvalidOnionKey
 		}
 	}
 
@@ -216,7 +216,7 @@ func (p *OnionProcessor) ExtractErrorEncrypter(r io.Reader) (ErrorEncrypter, lnw
 			return nil, lnwire.CodeInvalidOnionKey
 		default:
 			log.Errorf("unable to decode onion packet: %v", err)
-			return nil, lnwire.CodeTemporaryChannelFailure
+			return nil, lnwire.CodeInvalidOnionKey
 		}
 	}
 
@@ -232,7 +232,7 @@ func (p *OnionProcessor) ExtractErrorEncrypter(r io.Reader) (ErrorEncrypter, lnw
 			return nil, lnwire.CodeInvalidOnionKey
 		default:
 			log.Errorf("unable to process onion packet: %v", err)
-			return nil, lnwire.CodeTemporaryChannelFailure
+			return nil, lnwire.CodeInvalidOnionKey
 		}
 	}