message: Make set_local_tparam check role and state
  Do not let a value change once it has been sent.
diff: @@ -449,7 +449,15 @@ impl Connection {
  /// Set a local transport parameter, possibly overriding a default value.
  pub fn set_local_tparam(&self, key: u16, value: TransportParameter) {
  + if matches!(
  + (self.role(), self.state()),
  + (Role::Client, State::Init) | (Role::Server, State::WaitInitial)
  + ) {
  self.tps.borrow_mut().local.set(key, value)
  + } else {
  + qerror!("Cannot set local tparam when not in an initial connection state.");
  + qerror!("Current state: {:?}", self.state());
  + }
  }
  /// Set the connection ID that was originally chosen by the client.
  