MEDIUM: quic: refactor buffered STREAM ACK consuming

MEDIUM: quic: refactor buffered STREAM ACK consuming

For the moment, streamdesc layer can only deal with in-order ACK at the
stream level. Received out-of-order ACKs are buffered in a tree attached
to a streambuf instance.

Previously, caller of qc_stream_desc_ack() was responsible to implement
consumption of these buffered ACKs. Refactor this by implementing it
directly at the streamdesc layer within qc_stream_desc_ack(). This
simplifies quic_rx ACK handling and ensure buffered ACKs are consumed as
soon as possible.