The vnclisten parameter is ignored with hvm domains under xen-4.12.1 and FreeBSD-12.0

[Brian Buhrow]

	hello Roger.  thanks for the quick reply.  I think, after a careful
read of the xl.cfg man page plus a careful reading of the xen-tools source
code, I've figured out the issue.  I'm sending the solution here so folks
will have it in the future.

If one is configuring an hvm guest, any vfb specifications  in the domain
configuration are ignored.  Instead, the parameters that normally get placed
in a vfb stanza must be placed as top level configuration items.  For
example:

For a PV guest:
vfb = [ 'vnc=1,vnclisten=10.14.200.200' ]

Translates to, for an hvm guest:

vnc = 1
vnclisten = "10.14.200.200"

The xl.cfg man page doesn't say that in order for the vnc parameters to be
picked up for hvm guests with emulated graphics cards, those parameters
need to be specified as top level parameters in the config file.  It took
reading the source code of the xen-tools xl code to figure that out.

-thanks
-Brian