Ondřej Surý authored May 27, 2021 and Ondřej Surý committed May 31, 2021

Previously, dumping the zones to the files were quantized, so it doesn't
slow down network IO processing.  With the introduction of network
manager asynchronous threadpools, we can move the IO intensive work to
use that API and we don't have to quantize the work anymore as it the
file IO won't block anything except other zone dumping processes.

(cherry picked from commit 8a5c62de)