qemuDomainObjPrivate: Annotate 'allowReboot' field

Save further readers the headache of determining what it actually does
and note that it's not used with qemu version supporting the
'set-action' command.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

src/qemu/qemu_domain.h

@@ -154,6 +154,14 @@ struct _qemuDomainObjPrivate {
 
     bool fakeReboot;
     bool pausedShutdown;
+    /* allowReboot:
+     *
+     * Unused with new QEMU versions which have QEMU_CAPS_SET_ACTION.
+     *
+     * Otherwise if it's set to VIR_TRISTATE_BOOL_YES, QEMU was started with
+     * -no-shutdown, and if set to VIR_TRISTATE_BOOL_NO qemu was started with
+     * -no-reboot instead.
+     */
     virTristateBool allowReboot;
 
     int jobs_queued;