Currently realm_sync_socket_websocket_closed uses realm_web_socket_errno_e whereas realm_sync_socket_write_complete and other *_complete methods takes an realm_errno_e.
These methods are only used in the context of Websocket and should either return RLM_ERR_WEBSOCKET_OK or the corresponding RLM_ERR_WEBSOCKET_ one (example RLM_ERR_WEBSOCKET_WRITE_ERROR for realm_sync_socket_write_complete)