htlcswitch+router+server: handle payment error topology updates

In previous commits we have intoduced the onion errors. Some of this
errors include lnwire.ChannelUpdate message. In order to change
topology accordingly to the received error, from nodes where failure
have occured, we have to propogate the update to the router subsystem.

server.go

@@ -176,6 +176,10 @@ func newServer(listenAddrs []string, chanDB *channeldb.DB, cc *chainControl,
 
 			peer.localCloseChanReqs <- request
 		},
+		UpdateTopology: func(msg *lnwire.ChannelUpdate) error {
+			s.discoverSrv.ProcessRemoteAnnouncement(msg, nil)
+			return nil
+		},
 	})
 
 	// If external IP addresses have been specified, add those to the list