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