http2session.pendingSettingsAck
指示 Http2Session 当前是否正在等待已发送的 SETTINGS 帧的确认。
调用 http2session.settings() 方法后会是 true。
一旦所有发送的 SETTINGS 帧都被确认，将是 false。
Indicates whether the Http2Session is currently waiting for acknowledgment of
a sent SETTINGS frame. Will be true after calling the
http2session.settings() method. Will be false once all sent SETTINGS
frames have been acknowledged.