MEDIUM: proto_tcp: remove any dependence on stream_interface

MEDIUM: proto_tcp: remove any dependence on stream_interface

The last uses of the stream interfaces were in tcp_connect_server() and
could easily and more appropriately be moved to its callers, si_connect()
and connect_server(), making a lot more sense.

Now the function should theorically be usable for health checks.

It also appears more obvious that the file is split into two distinct
parts :
  - the protocol layer used at the connection level
  - the tcp analysers executing tcp-* rules and their samples/acls.