MINOR: log: Don't systematically set LW_REQ when a sample expr is added

When a log-format string is parsed, if a sample fetch is found, the flag LW_REQ
is systematically added on the proxy. Unfortunately, this produce a warning
during HAProxy start-up when a log-format string is used for a tcp-check send
rule. Now this flag is only added if the parsed sample fetch depends on HTTP
information.
1 file changed