Follow-up from "Resolve "memory leak when named attempts to listen on FreeBSD virtual interface""

The following discussion from !4823 (merged) should be addressed:

• @sgoldlust started a discussion:

  - If an outgoing packet exceeded max-udp-size, it was dropped instead
    of sending a proper response. To address this issue, the IP_DONTFRAG settings on
    UDP sockets, which were enabled during DNS Flag Day 2020, were rolled back.