CLEANUP: connection: split sock_ops into data_ops, app_cp and si_ops

CLEANUP: connection: split sock_ops into data_ops, app_cp and si_ops

Some parts of the sock_ops structure were only used by the stream
interface and have been moved into si_ops. Some of them were callbacks
to the stream interface from the connection and have been moved into
app_cp as they're the application seen from the connection (later,
health-checks will need to use them). The rest has moved to data_ops.

Normally at this point the connection could live without knowing about
stream interfaces at all.