title: TcpListener: Reject an incoming connection request before connection
body: <p>I have a service that's open to everyone on the public internet. It runs TcpListener to manage incoming connections.</p>
  
  <p>The service maintains a list of persistently misbehaving clients by their incoming IP address. Any connections coming from a listed IP are sent a "go away" message as the connection is closed down.</p>
  
  <p>I'd prefer it if the socket isn't opened in the first place, but by the time AcceptTcpClient has returned, the connection is already opened.</p>
  
  <p>Is there a way for my code to step in and examine incoming connection requests (and perhaps reject them) before they are opened?</p>
  
  <p>Many thanks.</p>