tools lib traceevent: Unregister handler when function 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 <[e-mail]>
Reviewed-by: Jiri Olsa <[e-mail]>
Acked-by: Steven Rostedt <[e-mail]>
Cc: Frederic Weisbecker <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Steven Rostedt <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/lib/traceevent/plugin_function.c

···
 {
 	int i, x;
 
+	pevent_unregister_event_handler(pevent, -1, "ftrace", "function",
+					function_handler, NULL);
+
 	for (i = 0; i <= cpus; i++) {
 		for (x = 0; x < fstack[i].size && fstack[i].stack[x]; x++)
 			free(fstack[i].stack[x]);