illumos gate

This change is already present in SmartOS and OmniOS.
Additionally, Jorge Schrauwen kindly applied the patch on top of SmartOS and re-tested, to double check there was no impact, and confirmed that it worked as expected.

I have ONUd to this patch and set up an OmniOS bhyve zone with and without a password set on the VNC server.

That is, once with -s 30:0,fbuf,vga=off,unix=/tmp/vm.vnc
and once with -s 30:0,fbuf,vga=off,unix=/tmp/vm.vnc,password=plod123

In the first case, I was able to connect to the VNC session without a password using Jolly's Fast VNC and the MacOS screen sharing client.
In the second, I was prompted for a password. An incorrect password was not accepted, the correct one was.