htlcswitch: notify outgoing link failures for local sends

Notify link failures for our own payments. Separate handling code is
required for local payment link failures because we do not pass these
failures back through the switch (like we do for link failures for
forwards), but rather send them straight back to the router. Our own
sends have the payment ID saved in the incoming htlc ID of the packet's
incoming circuit. This change replaces that value with for the sake
of consistent notifying of sends and receives from our node.

htlcswitch/switch.go

@@ -770,6 +770,20 @@ func (s *Switch) handleLocalDispatch(pkt *htlcPacket) error {
 	if htlc, ok := pkt.htlc.(*lnwire.UpdateAddHTLC); ok {
 		link, err := s.handleLocalAddHTLC(pkt, htlc)
 		if err != nil {
+			// Notify the htlc notifier of a link failure on our
+			// outgoing link. Incoming timelock/amount values are
+			// not set because they are not present for local sends.
+			s.cfg.HtlcNotifier.NotifyLinkFailEvent(
+				newHtlcKey(pkt),
+				HtlcInfo{
+					OutgoingTimeLock: htlc.Expiry,
+					OutgoingAmt:      htlc.Amount,
+				},
+				HtlcEventTypeSend,
+				err,
+				false,
+			)
+
 			return err
 		}