ERR_HTTP2_MAX_PENDING_SETTINGS_ACK

每当向已连接的对等方发送 HTTP/2 SETTINGS 帧时，对等方都必须发送确认，表明它已接收并应用了新的 SETTINGS。默认情况下，在任何给定时间可以发送的未确认 SETTINGS 帧数量是有限的。当达到该限制时，将使用此错误代码。

【Whenever an HTTP/2 SETTINGS frame is sent to a connected peer, the peer is required to send an acknowledgment that it has received and applied the new SETTINGS. By default, a maximum number of unacknowledged SETTINGS frames may be sent at any given time. This error code is used when that limit has been reached.】