The host notifier rework tried both to unify host notifiers across
transports and plug a possible hole during host notifier
re-assignment. Unfortunately, this meant a change in semantics that
breaks vhost and iSCSI+dataplane.
As the minimal fix, keep the common host notifier code but revert
to the old semantics so that we have time to figure out the proper
fix.
Fixes: 6798e245a3 ("virtio-bus: common ioeventfd infrastructure")
Reported-by: Peter Lieven <address@hidden>
Reported-by: Jason Wang <address@hidden>
Reported-by: Marc-André Lureau <address@hidden>
Signed-off-by: Cornelia Huck <address@hidden>