Include faulty TLV tag in InvalidOnionPayload error (#2908)

We have a couple of such errors in our logs for blinded payment relay,
and we currently don't know what the sender did wrong because we don't
log the faulty TLV tag. This should make it easier to debug.

eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/FailureMessage.scala

@@ -71,7 +71,7 @@ case class TrampolineExpiryTooSoon(tlvs: TlvStream[FailureMessageTlv] = TlvStrea
 case class FinalIncorrectCltvExpiry(expiry: CltvExpiry, tlvs: TlvStream[FailureMessageTlv] = TlvStream.empty) extends FailureMessage { def message = "payment expiry doesn't match the value in the onion" }
 case class FinalIncorrectHtlcAmount(amount: MilliSatoshi, tlvs: TlvStream[FailureMessageTlv] = TlvStream.empty) extends FailureMessage { def message = "payment amount is incorrect in the final htlc" }
 case class ExpiryTooFar(tlvs: TlvStream[FailureMessageTlv] = TlvStream.empty) extends FailureMessage { def message = "payment expiry is too far in the future" }
-case class InvalidOnionPayload(tag: UInt64, offset: Int, tlvs: TlvStream[FailureMessageTlv] = TlvStream.empty) extends Perm { def message = "onion per-hop payload is invalid" }
+case class InvalidOnionPayload(tag: UInt64, offset: Int, tlvs: TlvStream[FailureMessageTlv] = TlvStream.empty) extends Perm { def message = s"onion per-hop payload is invalid (tag=$tag)" }
 case class PaymentTimeout(tlvs: TlvStream[FailureMessageTlv] = TlvStream.empty) extends FailureMessage { def message = "the complete payment amount was not received within a reasonable time" }
 
 /**