When using large blocks like 1M, there will be more than UINT16_MAX qwords in
one block, so this ASSERT would go off. Also, it is possible for the histogram
to overflow. We cap them to UINT16_MAX to prevent this.
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#4257