lib/rules: fix a bug in subnet computations
The problem mainly affected subnets not aligned on whole bytes, but maybe also others. Reported: https://lists.nic.cz/hyperkitty/list/knot-resolver-users@lists.nic.cz/message/6P2JPK72WMVLP45TDV42DTACEA2N5NW2/
I'm really sorry about this; no idea why I thought that the simple multiplication would suffice.
FIXME: more review and testing, and perhaps also the comments.
Edited by Vladimír Čunát