hw/xen: Implement EVTCHNOP_close

It calls an internal close_port() helper which will also be used from
EVTCHNOP_reset and will actually do the work to disconnect/unbind a port
once any of that is actually implemented in the first place.

That in turn calls a free_port() internal function which will be in
error paths after allocation.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
3 files changed