MAX_FRAME_SIZE propagation in HTTP/2 client flow control

[spericas]

Problem Description

A SETTINGS frame can be received at any time during the lifetime of an HTTP/2 connection. If it includes a new MAX_FRAME_SIZE settings, it needs to be honored by all running streams. We handle this correctly for a reset of INITIAL_WINDOW_SIZE but not MAX_FRAME_SIZE. See HTTP2ClientConnection#handle for more details.

From the spec: When a new SETTINGS_MAX_FRAME_SIZE value is sent, the receiver must acknowledge the SETTINGS frame with a SETTINGS ACK. The new frame size limit takes effect after the sender receives that ACK.
Once active, the updated limit governs all frames sent on the connection — including those belonging to already-existing streams — except that frames already in flight before the ACK are still valid under the previous limit.