MINOR: frontend: Create HTTP txn for HTX streams

MINOR: frontend: Create HTTP txn for HTX streams

When an HTX stream is created, be sure to always create the HTTP txn object,
regardless of the ".http_needed" value of the frontend. That happens when a
destructive HTTP upgrades is performed (TCP>H2). The frontend is a TCP
proxy. If there is no dependency on the HTTP part, the HTTP transaction is
not created at this stage but only when the backend is set. For now, it is
not a problem. But an HTTP txn will be mandatory to fully support TCP to
HTTP upgrades after frontend tcp-request rules evaluation.