Revert "evtchn: refuse EVTCHNOP_status for Xen-bound event channels"

The commit makes a claim without justification.

The claim is false; it broke lsevtchn in dom0, a debugging utility which
absolutely does care about all of the domain's event channels.

Whether to return information about a xen-owned evtchn is a matter of policy,
and it's not acceptable to subvert Xen's security subsystem on the decision.

This reverts commit f60ab5337f.

Fixes: f60ab5337f ("evtchn: refuse EVTCHNOP_status for Xen-bound event channels")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Daniel P. Smith <dpsmith@apertussolutions.com>

xen/common/event_channel.c

@@ -1041,12 +1041,6 @@ int evtchn_status(evtchn_status_t *status)
 
     read_lock(&d->event_lock);
 
-    if ( consumer_is_xen(chn) )
-    {
-        rc = -EACCES;
-        goto out;
-    }
-
     rc = xsm_evtchn_status(XSM_TARGET, d, chn);
     if ( rc )
         goto out;