Hi Cesare, Thanks for report this bug! I've recently adopted this package and some important modifications have been made and it seems some mistakes also :)
The bug reported is related to the init script, indeed it has been recently deleted in upstream [1], so that commit will be cherry picked and applied to debian package, closing this bug. Regards, Alberto [1] https://git.netfilter.org/arptables/commit/?id=988d6a4cd1b12718177bf3065f07faeabb208713
