tools lib traceevent: Unregister handler when xen plugin is unloaded

The function handler should be unregistered when the plugin is unloaded
otherwise it'll try to access invalid memory.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Reviewed-by: Jiri Olsa <jolsa@redhat.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1389839478-5887-13-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/traceevent/plugin_xen.c

@@ -128,3 +128,9 @@ int PEVENT_PLUGIN_LOADER(struct pevent *pevent)
 				       PEVENT_FUNC_ARG_VOID);
 	return 0;
 }
+
+void PEVENT_PLUGIN_UNLOADER(struct pevent *pevent)
+{
+	pevent_unregister_print_function(pevent, process_xen_hypercall_name,
+					 "xen_hypercall_name");
+}