- windivert was being set up *before* DNS is set up, so the DNS port was
nullopt and thus we couldn't properly identify upstream DNS traffic.
- close() doesn't close a socket on Windows, so the socket-bind-close
approach to get a free UDP port wasn't actually closing, and thus
unbound upstream constrained to the given port were completely
failing.
- The unbound thread was accessing the same shared_ptr instance as the
outer code, which isn't thread-safe; changed it to copy a weak_ptr
into the lambda instead.
- Exclude upstream DNS traffic in the filter rather than capturing and
reinjecting it.