prevent memory leaks from duplicate/spurious qwx(4) fw memory requests
The request_mem_indication event handler would always allocate a new
buffer to store the firmware's request, potentially leaking an already
existing copy. Ensure that this buffer is always freed, and avoid
allocating it in the first place if we're not currently expecting this
event to occur.
All this would have surfaced the previously fixed bug with the missing
wakeup much earlier. The wakeup was always missed but when the driver
retried it would find the stale buffer from the previous event and not
even enter tsleep.