BUG/MINOR: mux-h2: Don't expect more HTX data on 1xx interim responses

BUG/MINOR: mux-h2: Don't expect more HTX data on 1xx interim responses

Commit b70921f2c ("BUG/MINOR: mux-h2: Properly handle full or truncated HTX
messages on shut") introduced a regression. When the response start-line had
the HTX_SL_F_XFER_LEN flag set, the H2 stream was flagged with
H2_SF_MORE_HTX_DATA, as if a payload was expected after the response
headers. This was also set for 1xx interim responses. If a final response
with an unknown length was received (no HTX_SL_F_XFER_LEN set), the flag
H2_SF_MORE_HTX_DATA was not removed, leading to an error. The H2 stream was
seen as truncated when a shut was performed and it was reset with a
RST_STREAM(CANCEL).

To fix the issue, H2_SF_MORE_HTX_DATA flag is no longer set for 1XX interim
responses.

This patch must be backported as far as 2.8.