SMPP Log Conversion Hook
This hook logs a message conversion event, either from SMPP to SMS or the reverse. The default logger implementation either log the event as "smpp to ec_message" or "ec_message to smpp". For MO, an "smpp to ec_message" event is logged; for MT, an "ec_message to smpp" event is logged. Overwrite this hook if you want to log message conversion differently.