BUG/MINOR: http-ana: Send the right error if max retries is reached on L7 retry

BUG/MINOR: http-ana: Send the right error if max retries is reached on L7 retry

This bug was introduced by the previous commit (9f5382e45 Revert "MEDIUM:
http-ana: Deal with L7 retries in HTTP analysers") because I failed the
revert.

On L7 retry, if the maximum connection retries is reached, an error must be
return to the client. Depending the situation, it may be a 502-Bad-Gateway
(empty-response or junk-response), a 504-Gateway-Timeout (response-timeout)
or a 425-Too-Early (0rtt-rejected). But contrary to what the comment says,
the do_l7_retry() function always returns a success.

Note it is not a problem for L7 retries on the response status code because
the stream-interface already takes care to have not reached the maximum
connection retries counter to trigger a L7 retry.

This patch must be backported to 2.4 because the commit must also be
backported to 2.4.