flow/timeout: use single packet for timeout handling

flow/timeout: use single packet for timeout handling

In the FlowFinish logic, one or two pseudo packets are used to finish flow
handling. In the case of 2 (one per direction), the logic first set up the
2 packets, then it would process them one by one. This lead to poor cache
locality.

This patch processes the first packet entirely first, followed by the second
packet.