Connection closed when inbound logon has a too-low sequence number

Created by: imirkin

This seems like a pretty common case ... someone loses their session, doesn't realize it, and is wondering why they don't get a response to a Logon / connection gets closed. Internally there's a log about the sequence number being too low, but it would be nice to provide that feedback to the other side.

Is there a strong reason why this isn't handled in logon_state.go? Would it be OK to return a rejection of some sort with the information that's logged? (Suggestions on how to best do that, or a different approach are most welcome.)