libxl: Set auto-allocated graphics ports to used on reconnect

libxl: Set auto-allocated graphics ports to used on reconnect

The libxl driver reconnects to all running VMs when libvirtd is restarted,
but it failed to mark auto-allocated graphics ports as set in the port
allocator. If many VMs are running that use port auto-allocation and
libvirtd is restarted, the port allocator is likely to hand out a port
already in use when a new VM is created that uses auto-allocation. VM
creation will fail due to the port clash.

When reconnecting to running VMs after a libvirtd restart, let the port
allocator know about previously allocated ports.

Signed-off-by: Jim Fehlig <jfehlig@suse.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>