MFC: sys/geom/geom_event.c 1.55
Delay an orphan event if provider has still in-flight I/O requests.
This way GEOM classes can safely detach from provider when an orphan
event is received. This fixes 'detach with active requests' panic for
gstripe/gconcat under load.
PR: kern/102766
Submitted by: mjacob
OK'ed by: phk
Approved by: re (mux)