Fix invalid rogue peer delay request error

[GeorgeKT]

When linuxptp goes from LISTENING to UNCALIBRATED, it will flush the the peer delay. This means that linuxptp forgets it sent a peer delay request. However, if there is an outstanding peer delay request at this point in time, the subsequent response will be considered rogue, and linuxptp will go into a faulty state. Which causes it to do nothing for a while.

To fix this, we keep track of wether a flush_peer_delay has occurred. And if we receive a response after one, we don't consider it rogue but just ignore it.