Adapter leaks requests when mpt_event_notify_reply() has to acknowledge
an event leading to "adapter resource shortage" messages when the scsipi
subsystem tries to use all adapt_openings.

Change mpt_ctlop() to free the request on event MPI_FUNCTION_EVENT_ACK.

Tested on a SunFire X4275 with Symbios Logic SAS1068E (1000:0058, rev. 4).

(hannken)