MFC r274477: Fix check for vendor-specific peripheral qualifier.

Submitted by:	anton.rang@isilon.com
MFC r274154, r274163:
Add to CTL support for logical block provisioning threshold notifications.

For ZVOL-backed LUNs this allows to inform initiators if storage's used or
available spaces get above/below the configured thresholds.

Sponsored by:	iXsystems, Inc.