MINOR: Add TO/FROM_SET flags to struct stream_interface

[WT: it will make sense to remove SN_FRT_ADDR_SET and to use these
  flags everywhere instead ]
diff --git a/include/types/stream_interface.h b/include/types/stream_interface.h
index 8f35d64..dae36ef 100644
--- a/include/types/stream_interface.h
+++ b/include/types/stream_interface.h
@@ -73,6 +73,8 @@
 	SI_FL_INDEP_STR  = 0x0040,  /* independant streams = don't update rex on write */
 	SI_FL_NOLINGER   = 0x0080,  /* may close without lingering. One-shot. */
 	SI_FL_SRC_ADDR   = 0x1000,  /* get the source ip/port with getsockname */
+	SI_FL_TO_SET     = 0x2000,  /* addr.to is set */
+	SI_FL_FROM_SET   = 0x4000,  /* addr.from is set */
 };
 
 /* target types */