MEDIUM: connection: Rely on addresses at stream level to make proxy line

MEDIUM: connection: Rely on addresses at stream level to make proxy line

If the stream exists, the frontend stream-interface is used to get the
client source and destination addresses when the proxy line is built. For
now, stream-interface or session addresses are never set. So, thanks to the
fallback mechanism, no changes are expected with this patch. But its purpose
is to rely on addresses at the appropriate level when set instead of those
at the connection level.