new: usr: implement the 'request-ixfr-max-diffs' configuration option
The new 'request-ixfr-max-diffs' configuration option sets the maximum number of incoming incremental zone transfer (IXFR) differences, exceeding which triggers a full zone transfer (AXFR).
Closes #4389 (closed)
Edited by Arаm Sаrgsyаn