modules/rtu: produce response to every request when swcore stops acking them due to lack of pages

When IB in the swcore was stuck waiting for the start page allocation, port
fsm in the RTU was stuck in S_FINAL_MASK. If one new request managed to
arrive before endpoint got rtu_full signal, the response for that
request was lost. The result was misaligmnet of the rtu decisions with
frames in the IB of the swcore.