routing+routerrpc: improve prob. estimation for untried connections

This commit changes mission control to partially base the estimated
probability for untried connections on historical results obtained in
previous payment attempts. This incentivizes routing nodes to keep all
of their channels in good shape.

server.go

@@ -660,6 +660,7 @@ func newServer(listenAddrs []net.Addr, chanDB *channeldb.DB,
 			AprioriHopProbability: routingConfig.AprioriHopProbability,
 			PenaltyHalfLife:       routingConfig.PenaltyHalfLife,
 			MaxMcHistory:          routingConfig.MaxMcHistory,
+			AprioriWeight:         routingConfig.AprioriWeight,
 		},
 	)
 	if err != nil {