MINOR: stream-int: use conn_get_{src,dst} in conn_si_send_proxy()

These ones replace the previous conn_get_{from,to}_addr() used to wait
for the connection establishment before sending a LOCAL line. The
error handling was preserved.
diff --git a/src/stream_interface.c b/src/stream_interface.c
index 9b9a8e9..75e60ff 100644
--- a/src/stream_interface.c
+++ b/src/stream_interface.c
@@ -381,12 +381,7 @@
 			/* The target server expects a LOCAL line to be sent first. Retrieving
 			 * local or remote addresses may fail until the connection is established.
 			 */
-			conn_get_from_addr(conn);
-			if (!(conn->flags & CO_FL_ADDR_FROM_SET))
-				goto out_wait;
-
-			conn_get_to_addr(conn);
-			if (!(conn->flags & CO_FL_ADDR_TO_SET))
+			if (!conn_get_src(conn) || !conn_get_dst(conn))
 				goto out_wait;
 
 			ret = make_proxy_line(trash.area, trash.size,