MINOR: stream_interface: add a client target : TARG_TYPE_CLIENT

This one will be used to identify the direction the SI is being used. All
incoming connections have a target of type TARG_TYPE_CLIENT.
diff --git a/include/types/stream_interface.h b/include/types/stream_interface.h
index fb2b258..2c57acd 100644
--- a/include/types/stream_interface.h
+++ b/include/types/stream_interface.h
@@ -80,6 +80,7 @@
 /* target types */
 enum {
 	TARG_TYPE_NONE = 0,         /* no target set, pointer is NULL by definition */
+	TARG_TYPE_CLIENT,           /* target is a client, pointer is NULL by definition */
 	TARG_TYPE_PROXY,            /* target is a proxy   ; use address with the proxy's settings */
 	TARG_TYPE_SERVER,           /* target is a server  ; use address with server's and its proxy's settings */
 	TARG_TYPE_APPLET,           /* target is an applet ; use only the applet */