fix: add edns-buffer-size script
This PR is related to https://gitlab.nic.cz/turris/turris-os-packages/-/merge_requests/586
It adds fix script to convert edns_buffer_size default value from 4096
to 1232
. In case that edns_buffer_size value not equal to 4096 we don't do anything because it was changed by the user.
This change is related to DNS Flag Day 2020 https://dnsflagday.net/2020/#dns-flag-day-2020
Run tested on HBK
Edited by Jan Pavlinec