3580 Want zvols to return volblocksize when queried for physical block size
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Dan Kimmel <dan.kimmel@delphix.com>
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: Boris Protopopov <boris.protopopov@nexenta.com>
Reviewed by: Garrett D'Amore <garrett@damore.org>
Approved by: Gordon Ross <gwr@nexenta.com>
	[illumos-gate merge]

commit a0b60564dfc644f4bfaef1ce26d343b44cf68bc5
    3580 Want zvols to return volblocksize when queried for physical block size