Add blocking via NFQUEUE

[ckcr4lyf]

The netfilter project introduced libfilter_nfqueue allowing userspace applications to make decisions on accepting or dropping packets (including modifying them).

Currently, sni-log just captures packets via libpcap. However, it is possible to also pass packets to it if it subscribes to a NFQUEUE, and then it can make decisions based on the domain (after parsing the SNI)

A good rust PoC is here: https://github.com/chifflier/nfqueue-rs/blob/master/examples/nfq-example.rs (note: running the example requires upgraded dependencies, or this PR to me merged: chifflier/nfqueue-rs#20)

This application could then be configured to block certain domains via SNI , through a flag of some sort. (As opposed to just logging them)

[ckcr4lyf]

Note: This would probably not work on Mac, and almost certainly not on Windows.