routing: modify findRoute to accept starting node as a paramter

This commit slightly modified findRoute to accept the node which should
be used as the starting point in our path finding algorithm. With this
change, as we move to a k-shortest paths algorithm this modification
will be needed as all of our path finding attempts won’t always
originate from a the same starting point.

routing/router.go

@@ -1068,7 +1068,7 @@ func (r *ChannelRouter) FindRoute(target *btcec.PublicKey, amt btcutil.Amount) (
 	}
 
 	// TODO(roasbeef): add k-shortest paths
-	route, err := findRoute(r.cfg.Graph, target, amt)
+	route, err := findRoute(r.cfg.Graph, r.selfNode, target, amt)
 	if err != nil {
 		log.Errorf("Unable to find path: %v", err)
 		return nil, err