MINOR: log: provide sending log context to process_send_log() when available

MINOR: log: provide sending log context to process_send_log() when available

This is another prerequisite work in preparation for log-profiles: in this
patch we make process_send_log() aware of the log origin, primarily aiming
for sess and txn logging steps such as error, accept, connect, close, as
well as relevant sess and stream pointers.