MINOR: mux-quic: refactor snd_buf

Factorize common code between h3 and hq-interop snd_buf operation. This
is inserted in MUX QUIC snd_buf own callback.

The h3/hq-interop API has been adjusted to directly receive a HTX
message instead of a plain buf. This led to extracting part of MUX QUIC
snd_buf in qmux_http module.

This should be backported up to 2.6.
6 files changed