edns behaviour on forward only configuration
Description
I would like is a way to fix the advertised payload and guarantee it will always stayed fixed because I know my environment and I don't need BIND to try and work out what the forwarders or the intervening will permit.
- Use existing settings to infer how EDNS payload advertisement should work. e.g. if 'forward only' is enabled, don't do slow start. The danger with this is there might be a use case that needs both. or
- A new configuration parameter e.g. 'edns-udp-behaviour' that takes arguments "fixed" or "auto"
see RT #16201