evtchn: clear xen_consumer when clearing state

evtchn: clear xen_consumer when clearing state

Freeing a xen event channel would clear xen_consumer before clearing
the channel state, leaving a window where the channel is in a funny
state (still bound but no consumer).

Move the clear of xen_consumer into free_evtchn() where the state is
also cleared.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Ditch the pointless evtchn_close() wrapper around __evtchn_close()
(renaming the latter) as well as some bogus casts of function results
to void.

Signed-off-by: Jan Beulich <jbeulich@suse.com>