perf tools: No need to unconditionally read the max_stack sysctls

Let tools that need to have those variables with the sysctl current
values use a function that will read them.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-1ljj3oeo5kpt2n1icfd9vowe@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index 3c061c5..7a349fc 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -1264,7 +1264,7 @@ int cmd_top(int argc, const char **argv)
 			.proc_map_timeout    = 500,
 			.overwrite	= 1,
 		},
-		.max_stack	     = sysctl_perf_event_max_stack,
+		.max_stack	     = sysctl__max_stack(),
 		.sym_pcnt_filter     = 5,
 		.nr_threads_synthesize = UINT_MAX,
 	};