Change the default value for nocookie-udp-size back to 4096

Change the default value for nocookie-udp-size back to 4096

The DNS Flag Day 2020 reduced all the EDNS buffer sizes to 1232.  In
this commit, we revert the default value for nocookie-udp-size back to
4096 because the option is too obscure and most people don't realize
that they also need to change this configuration option in addition to
max-udp-size.