zvol: Cleanup set property

zvol_set_volmode() and zvol_set_snapdev() share a common code path.
Merge this shared code path into zvol_set_common().

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Ameer Hamza <ahamza@ixsystems.com>
Closes #15409