The event handler calls scsi_scan_host() when events are missed, which will
hotplug new LUNs.  However, this function won't remove any unplugged LUNs.
The result is that hotunplug doesn't work properly when the number of
unplugged LUNs exceeds the event queue size (currently 8).

Scan existing LUNs when events are missed to check if they are still
present.  If not, remove them.

Link: https://lore.kernel.org/r/20190905181903.29756-1-mlupfer@ddn.comSigned-off-by: Matt Lupfer <mlupfer@ddn.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>