Lack of swatches

[LeonJung]

Hi, all

As we have a talk in the thread ros-navigation/navigation2#682 about the navigation stack, I found that there is lack of swatch error occurs from the setting line here.

Since there are many use cases with turtlebot3, only a few people who uses another lidar which has a long range sight must be having trouble with that setting. (I'm using sick571, so the rviz stops running when swatch goes to 8).

I set this from 4 to 256 to avoid the error in running rviz. Of course who needs more swatches should change this value over more, but I think that this is not a generalized way to solve.

Do you have any ideas?