MINOR: mux-h1: Handle RAW_DATA blocks when sending data

MINOR: mux-h1: Handle RAW_DATA blocks when sending data

Tunneled data are now stored in RAW_DATA blocks. The H1 multiplexer must be
able to send them. h1_make_tunnel() is responsible to do so.

For the H1 multiplexer, there is no difference with HTTP data: both are sent
verbatim. Only the ability to handle the new type is added here. No producer
emits such block yet so h1_make_tunnel() relies on htx_is_data_type() for
now. But once all changes done, this will have to be modified to accept
RAW_DATA blocks only.