routing+routerrpc: take max cltv limit into account within path finding

With the introduction of the max CLTV limit parameter, nodes are able to
reject HTLCs that exceed it. This should also be applied to path
finding, otherwise HTLCs crafted by the same node that exceed it never
left the switch. This wasn't a big deal since the previous max CLTV
limit was ~5000 blocks. Once it was lowered to 1008, the issue became
more apparent. Therefore, all of our path finding attempts now have a
restriction of said limit in in order to properly carry out HTLCs to the
network.

rpcserver.go

@@ -501,10 +501,11 @@ func newRPCServer(s *server, macService *macaroons.Service,
 
 			return info.NodeKey1Bytes, info.NodeKey2Bytes, nil
 		},
-		FindRoute:       s.chanRouter.FindRoute,
-		MissionControl:  s.missionControl,
-		ActiveNetParams: activeNetParams.Params,
-		Tower:           s.controlTower,
+		FindRoute:        s.chanRouter.FindRoute,
+		MissionControl:   s.missionControl,
+		ActiveNetParams:  activeNetParams.Params,
+		Tower:            s.controlTower,
+		MaxTotalTimelock: cfg.MaxOutgoingCltvExpiry,
 	}
 
 	var (
@@ -2940,7 +2941,7 @@ func (r *rpcServer) unmarshallSendToRouteRequest(
 type rpcPaymentIntent struct {
 	msat              lnwire.MilliSatoshi
 	feeLimit          lnwire.MilliSatoshi
-	cltvLimit         *uint32
+	cltvLimit         uint32
 	dest              route.Vertex
 	rHash             [32]byte
 	cltvDelta         uint16
@@ -2987,10 +2988,14 @@ func extractPaymentIntent(rpcPayReq *rpcPaymentRequest) (rpcPaymentIntent, error
 		payIntent.outgoingChannelID = &rpcPayReq.OutgoingChanId
 	}
 
-	// Take cltv limit from request if set.
-	if rpcPayReq.CltvLimit != 0 {
-		payIntent.cltvLimit = &rpcPayReq.CltvLimit
+	// Take the CLTV limit from the request if set, otherwise use the max.
+	cltvLimit, err := routerrpc.ValidateCLTVLimit(
+		rpcPayReq.CltvLimit, cfg.MaxOutgoingCltvExpiry,
+	)
+	if err != nil {
+		return payIntent, err
 	}
+	payIntent.cltvLimit = cltvLimit
 
 	if len(rpcPayReq.DestTlv) != 0 {
 		var err error