If an NS RRset at the parent side of a delegation point only contains
in-bailiwick NS records, at least one glue record should be included in
every referral response sent for such a delegation point or else clients
will need to send follow-up queries in order to determine name server
addresses. In certain edge cases (when the total size of a referral
response without glue records was just below to the UDP packet size
limit), named failed to adhere to that rule by sending non-truncated,
glueless referral responses.
Add tests attempting to trigger that bug in several different scenarios,
covering all possible combinations of the following factors:
- type of zone (signed, unsigned),
- glue record type (A, AAAA, both).
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