message: UDP associations' default timeout to be 15 seconds
  ref
diff: @@ -71,4 +71,8 @@ mod utils;
  pub const MAXIMUM_UDP_PAYLOAD_SIZE: usize = 65536;
  /// Default association expire time
  -pub const DEFAULT_TIMEOUT: Duration = Duration::from_secs(5 * 60);
  +///
  +/// FIXME: It is very hard to decide how long this value should be.
  +/// For some usecases, clients may open a socket for sending just one packet,
  +/// which will eventually cause too many *useless* associations are kept in the server.
  +pub const DEFAULT_TIMEOUT: Duration = Duration::from_secs(15);
  