MEDIUM: http: wait for the first chunk or message body length in http_process_body

MEDIUM: http: wait for the first chunk or message body length in http_process_body

This is the continuation of previous patch. Now that full buffers are
not rejected anymore, let's wait for at least the advertised chunk or
body length to be present or the buffer to be full. When either
condition is met, the message processing can go forward.

Thus we don't need to use url_param_post_limit anymore, which was passed
in the configuration as an optionnal <max_wait> parameter after the
"check_post" value. This setting was necessary when the feature was
implemented because there was no support for parsing message bodies.

The argument is now silently ignored if set in the configuration.