MINOR: h1-htx: Move HTTP chunks parsing into a dedicated function

MINOR: h1-htx: Move HTTP chunks parsing into a dedicated function

Chunked data are now parsed in a dedicated function. This way, it will be
possible to have two functions to parse chunked messages. The current one
for messages with large chunks and an other one to parse messages with small
chunks.

The parsing of small chunks is really sensitive because it may be used as a
DoS attack. So we must be carefull to have an optimized function to parse
such messages.