MFV r316926:
7955 libshare needs to initialize only those datasets being modified by the consumer

illumos/illumos-gate@8a981c3356b194b3b5c0ae9276a9cc31cd2f93a3
https://github.com/illumos/illumos-gate/commit/8a981c3356b194b3b5c0ae9276a9cc31cd2f93a3

https://www.illumos.org/issues/7955

Libshare currently initializes all available filesystems when doing any
libshare operation. This requires iterating through all the filesystem
multiple times, which is a huge performance problem for sharing and
unsharing operations.

Reviewed by: Steve Gonczi <steve.gonczi@delphix.com>
Reviewed by: Sebastien Roy <sebastien.roy@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed by: Yuri Pankov <yuri.pankov@gmail.com>
Approved by: Gordon Ross <gordon.w.ross@gmail.com>
Author: Daniel Hoffman <dj.hoffman@delphix.com>

For FreeBSD this is practically a NOP, just a diff reduction.