Implement some DNS Grease methods

Have named send requests which exercise parts to the DNS protocol that are not currently being exercised. This functionality is known as greasing.

Set the final reserved DNS header flag bit. This should be ignored by receivers and not be set in the reply. Log if seen in the reply. Disable Jan 1, 2026 to prevent the flag bit not being able to be used in the future due to greasing.

Set a current MBZ EDNS flag bit. This should be ignored by receivers and not be set in the reply. Log if seen in the reply. Disable Jan 1, 2026 to prevent the flag bit not being able to be used in the future due to greasing.

Test EDNS version negotiation. Send a high (100) EDNS version and check that BADVERS is returned if an OPT record is present and that the received version is 0.

Add a logging channel (grease) and named.conf controls to disable at options, view and server levels.

Document

ID for reference: https://datatracker.ietf.org/doc/draft-huque-dnsop-grease/