For inline-signed zones, the value of "ixfr-from-differences" is
hardcoded to:
- "yes" for the raw version of the zone,
- "no" for the signed version of the zone.
In other words, any user-provided "ixfr-from-differences" setting is
effectively ignored for an inline-signed zone. Ensure the user is aware
of that by adding a note to the ARM and logging a message when an
"ixfr-from-differences" option is found at the zone level.
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