MINOR: stream-int: set flag SI_FL_CLEAN_ABRT when mux supports clean aborts

By copying the info in the stream interface that the mux cleanly reports
aborts, we'll have the ability to check this flag wherever needed regardless
of the presence of a mux or not.
diff --git a/include/types/stream_interface.h b/include/types/stream_interface.h
index 95cf47a..0c83759 100644
--- a/include/types/stream_interface.h
+++ b/include/types/stream_interface.h
@@ -74,6 +74,7 @@
 	SI_FL_SRC_ADDR   = 0x1000,  /* get the source ip/port with getsockname */
 	SI_FL_WANT_PUT   = 0x2000,  /* an applet would like to put some data into the buffer */
 	SI_FL_WANT_GET   = 0x4000,  /* an applet would like to get some data from the buffer */
+	SI_FL_CLEAN_ABRT = 0x8000,  /* SI_FL_ERR is used to report aborts, and not SHUTR */
 };
 
 /* A stream interface has 3 parts :