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.
diff --git a/include/proto/proto_tcp.h b/include/proto/proto_tcp.h
index cdc1d37..5b6bf44 100644
--- a/include/proto/proto_tcp.h
+++ b/include/proto/proto_tcp.h
@@ -30,7 +30,7 @@
 int tcp_bind_socket(int fd, int flags, struct sockaddr_storage *local, struct sockaddr_storage *remote);
 void tcpv4_add_listener(struct listener *listener);
 void tcpv6_add_listener(struct listener *listener);
-int tcp_connect_server(struct stream_interface *si);
+int tcp_connect_server(struct connection *conn, int data);
 int tcp_connect_probe(struct connection *conn);
 int tcp_get_src(int fd, struct sockaddr *sa, socklen_t salen, int dir);
 int tcp_get_dst(int fd, struct sockaddr *sa, socklen_t salen, int dir);