MEDIUM: stream_interface: offer a generic function for connection updates

We need to have a generic function to be called by upper layers when buffer
flags have been updated (the si->update function). At the moment, both sock_raw
and sock_ssl had their own which basically was a copy-paste. Since these
functions are only used to update stream interface flags, it is logical to
have them handled by the stream interface code.

This allowed us to remove the stream_interface-specific update function from
sock_raw and sock_ssl which now use the generic code.

The stream_sock_update_conn callback has also been more appropriately renamed
conn_notify_si() since it's meant to be called by lower layers to notify the
SI and possibly upper layers about incoming changes.
diff --git a/include/proto/stream_interface.h b/include/proto/stream_interface.h
index 224ce84..5e2d74f 100644
--- a/include/proto/stream_interface.h
+++ b/include/proto/stream_interface.h
@@ -35,7 +35,8 @@
 void stream_int_report_error(struct stream_interface *si);
 void stream_int_retnclose(struct stream_interface *si, const struct chunk *msg);
 int conn_si_send_proxy(struct connection *conn, unsigned int flag);
-void stream_sock_update_conn(struct connection *conn);
+void conn_notify_si(struct connection *conn);
+void stream_int_update_conn(struct stream_interface *si);
 int stream_int_shutr(struct stream_interface *si);
 int stream_int_shutw(struct stream_interface *si);