cnct: parse onion for resolvers

With the introduction of additional payload fields for mpp, it becomes
a necessity to have their values available in the on-chain resolution
flow. The incoming contest resolver notifies the invoice registry of the
arrival of a payment and needs to supply all parameters for the registry
to validate the htlc.

server.go

@@ -906,6 +906,7 @@ func newServer(listenAddrs []net.Addr, chanDB *channeldb.DB,
 		Sweeper:             s.sweeper,
 		Registry:            s.invoices,
 		NotifyClosedChannel: s.channelNotifier.NotifyClosedChannelEvent,
+		OnionProcessor:      s.sphinx,
 	}, chanDB)
 
 	s.breachArbiter = newBreachArbiter(&BreachConfig{