Fix 32-bit maximum volume size

A limit of 1TB exists for zvols on 32-bit systems. Update the code
to correctly reflect this limitation in a similar manor as the
OpenZFS implementation.

Reviewed-by: Tom Caputi <tcaputi@datto.com>
Reviewed-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #5347