BUG/MINOR: http-ana: call the http_reset filter callback on L7 retries

BUG/MINOR: http-ana: call the http_reset filter callback on L7 retries

The filters documentation says that the http_reset callback is called
when the request is sent again to the server for a L7 retry, but it was
only called for the 1xx informational responses. It was documented with
the L7 retries in commit a254a37ad ("MEDIUM: streams: Add the ability to
retry a request on L7 failure."), but never called on this path.

do_l7_retry() now calls it for the response, once sc_reset_endp()
succeeded so that the retry is certain, and before the L7 buffer swap,
while the failed response is still in the buffer and txn->status is
set, like for the 1xx responses. The request is sent again as is from
the L7 buffer and its callbacks are not called again, so it is not
reset. The documentation now tells it.

This patch could be backported to all stable versions.

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