perf top: Don't look for kernel idle symbols in all DSOs

The 'top' tool initially supported only kernel symbols, when making it
support userspace symbols we forgot to make the symbol filter first
check that the DSO is the kernel one. Fix it.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
 c: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-54haztkeigmbump5sexxnzhv@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-top.c

@@ -623,10 +623,12 @@ static void *display_thread(void *arg)
 	return NULL;
 }
 
-static int symbol_filter(struct map *map __maybe_unused, struct symbol *sym)
+static int symbol_filter(struct map *map, struct symbol *sym)
 {
 	const char *name = sym->name;
 
+	if (!map->dso->kernel)
+		return 0;
 	/*
 	 * ppc64 uses function descriptors and appends a '.' to the
 	 * start of every instruction address. Remove it.

tools/perf/util/symbol.c

@@ -523,6 +523,10 @@ struct process_kallsyms_args {
 	struct dso *dso;
 };
 
+/*
+ * These are symbols in the kernel image, so make sure that
+ * sym is from a kernel DSO.
+ */
 bool symbol__is_idle(struct symbol *sym)
 {
 	const char * const idle_symbols[] = {