Replace direct marker-to-tail manipulation with per-sublist boolean
flags consumed lazily by feed threads. Each scanning thread resets its
own marker when it sees the flag, rather than having another thread
manipulate the marker directly.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com>
Signed-off-by: Ameer Hamza <ahamza@ixsystems.com>
Closes#18289