[NCSF] Minor code changes to reduce code duplication.

* Made a function in the Override struct to centralize where it
determines whether to use the override value or not.
* Made a function that returns the number of bytes that a command needs,
and used that to remove all the conditionals for processing a command to
instead handle that within the IF command itself.
Thanks to fincs and Henke37 for the suggestions to do this.