[illumos-Developer] Review --> iSCSI UNMAP support

[Dan McDonald]

Hello again!

Sumit Gupta contributed some iSCSI changes so that we can support the UNMAP
SCSI command.  This helps with ZFS sparse volumes servicing virtualized
clients.

Here's the webrev:

	http://www.kebe.com/~danmcd/webrevs/unmap/

and I can produce the test programs upon request.  I need to do some interop
testing with Linux and an ext4 filesystem (coming soon), but I figure this is
in good enough shape for you guys to take a peek.

Thanks!
Dan