6370 ZFS send fails to transmit some holes Reviewed by: Matthew Ahrens <mahrens@delphix.com> Reviewed by: Chris Williamson <chris.williamson@delphix.com> Reviewed by: Stefan Ring <stefanrin@gmail.com> Reviewed by: Steven Burgess <sburgess@datto.com> Reviewed by: Arne Jansen <sensille@gmx.net> Approved by: Robert Mustacchi <rm@joyent.com>