Some BGP implementations like goBGP send peer-down reason code as 0 while restarting or e.t.c. So peer-down should be recorded instead of discarded.
Added peer-down support for RFC9069 which includes VRF information in TLV.
Added support for better peer-down reason handling with unmarshalling BGP notification messages. TODO: may we need more coding for suberror codes like FSM errors?
Added peer-down reason description to the message types and peer-down structure.