REORG: stream-interface: move sock_raw_read() to si_conn_recv_cb()

The recv function is now generic and is usable to iterate any connection-to-buf
reading function from a stream interface. So let's move it to stream-interface.
diff --git a/include/proto/stream_interface.h b/include/proto/stream_interface.h
index 909d040..4f45c12 100644
--- a/include/proto/stream_interface.h
+++ b/include/proto/stream_interface.h
@@ -41,6 +41,7 @@
 int stream_int_shutw(struct stream_interface *si);
 void stream_int_chk_rcv_conn(struct stream_interface *si);
 void stream_int_chk_snd_conn(struct stream_interface *si);
+void si_conn_recv_cb(struct connection *conn);
 void si_conn_send_cb(struct connection *conn);
 void stream_sock_read0(struct stream_interface *si);