nodogsplash: simplify append_config_option

nodogsplash: simplify append_config_option

Drop arguement config_counterpart from append_config_option(). append_config_option
took an additional argument named config_counterpart which represents the
configuration name in configfile.This is needed for configuration variable names isn't the same
as in uci. Nodogsplash ignores the case of configuration variables and makes this feature optional.
Introduce new func append_config_option_map() which does the old behaviour.