fin method
Shutdown (FIN?): close the peer-to-peer session.
request is optional farewell data.
Returns a FIN? packet to the peer.
Implementation
DirectPacket fin(Uint8List? request) => DirectPacket.create(
ack: 0,
sn: 0,
index: 0,
count: 1,
command: Command.FIN,
payload: request,
);