MEDIUM: stream_sock: add a get_src and get_dst callback and remove SN_FRT_ADDR_SET

These callbacks are used to retrieve the source and destination address
of a socket. The address flags are not hold on the stream interface and
not on the session anymore. The addresses are collected when needed.

This still needs to be improved to store the IP and port separately so
that it is not needed to perform a getsockname() when only the IP address
is desired for outgoing traffic.
diff --git a/include/types/stream_interface.h b/include/types/stream_interface.h
index dae36ef..271abc7 100644
--- a/include/types/stream_interface.h
+++ b/include/types/stream_interface.h
@@ -133,6 +133,8 @@
 	void (*chk_snd)(struct stream_interface *);/* chk_snd function */
 	int  (*connect)(struct stream_interface *); /* connect function if any */
 	void (*release)(struct stream_interface *); /* handler to call after the last close() */
+	int (*get_src)(int, struct sockaddr *, socklen_t *); /* syscall used to retrieve src addr */
+	int (*get_dst)(int, struct sockaddr *, socklen_t *); /* syscall used to retrieve dst addr */
 
 	/* struct members below are the "remote" part, as seen from the buffer side */
 	struct target target;	/* the target to connect to (server, proxy, applet, ...) */