tracetool: dtrace disabled-events fix

If there are "disabled" entries in the trace-events file then
linetod_nop() is called if the backend is dtrace, it's currently
not present. Also equivalent fix for stap.

Signed-off-by: Lee Essen <lee.essen@nowonline.co.uk>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

scripts/tracetool

@@ -161,6 +161,18 @@ linetoc_nop()
     return
 }
 
+linetod_nop()
+{
+    # Used when "disabled" events are processed
+    return
+}
+
+linetostap_nop()
+{
+    # Used when "disabled" events are processed
+    return
+}
+
 linetoc_end_nop()
 {
     return