BUG/MEDIUM: mux-h1: use per-direction flags to indicate transitions

BUG/MEDIUM: mux-h1: use per-direction flags to indicate transitions

The H1 mux needs to store some information regarding the states that
were met (EOD, trailers, etc) for each direction but currently uses
only one set of flags. This results in failures when both the request
and the response use chunked-encoding because some elements are believed
to have been met already and a trailing 0 CRLF or just a CRLF may be
missing at the end.

The solution here consists in splitting these flags per direction, one
set for input processing and another set for output processing. Only
two flags were affected so this is not a big deal.

This needs to be backported to 1.9.