Fix segfault on receiving PoliteDisconnect

CPnpAdapter removes itself from the adapter factory as soon as it
receives a PoliteDisconnect notice. At this point it still has an
outstanding asynchronous operation. The adapter will be destroyed
before its buffer is used. The adapter can prevent this by taking
a ref.
testing: device timings should not have been increased
DEV_PNP_TIMEOUT should be in milliseconds