MEDIUM: mux-h1: Properly handle state transitions of chunked outgoing messages

MEDIUM: mux-h1: Properly handle state transitions of chunked outgoing messages

On the sending path, there are 3 states for chunked payload in H1:

  * H1_MSG_CHUNK_SIZE: the chunk size must be emitted
  * H1_MSH_CHUNK_CRLF: The end of the chunk must be emitted
  * H1_MSG_DATA: Chunked data must be emitted

However, some shortcuts were used on the sending path to avoid some
transitions. Especially, outgoing messages were never switched in
H1_MSG_CHUNK_SIZE state.

However, it will be necessary to properly handle all transitions on the payload
to implement mux-to-mux forwarding, to be sure to always known when the chunk
size or the end of the chunk must be emitted.