Someone came to me and pointed out that you could pretty
readily cause the refreservation calculation to exceed
2**64, given the 2**17 multiplier in it, and produce
refreservations wildly less than the actual volsize in cases where
it should have failed.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rich Ercolani <rincebrain@gmail.com>
Closes#15996