DOC: filters: channel_start_analyze is called again on L7 retries

DOC: filters: channel_start_analyze is called again on L7 retries

The filters documentation says that the flt_start_analyze and
flt_end_analyze analyzers are called only once per stream. On a L7
retry, the response analyzers are set again when the connection is
established, so channel_start_analyze is called a second time on the
response channel, without a channel_end_analyze call in between. It is
preceded by an http_reset call on the response.

Signed-off-by: Aleksandar Lazic <al-haproxy@none.at>