util: macmap: Convert to use GSList for storing macs instead of string lists

util: macmap: Convert to use GSList for storing macs instead of string lists

Since adding and removing is the main use case for the macmap module,
convert the code to a more efficient data structure.

The refactor also optimizes the loading from file where previously we'd
do a hash lookup + list lenght calculation for every entry.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>