Unfortunately, even after e79b6807, I still, much more rarely,
tripped asserts when playing with many ctldir mounts at once.
Since this appears to happen if we dispatched twice too fast, just
ignore it. We don't actually need to do anything if someone already
started doing it for us.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rich Ercolani <rincebrain@gmail.com>
Closes#14462
426d07d64c