selftests/ftrace: Add stacktrace ftrace filter command testcase

Add a test case for stacktrace filter command for ftrace.
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>

tools/testing/selftests/ftrace/test.d/ftrace/func-filter-stacktrace.tc

+#!/bin/sh
+# SPDX-License-Identifier: GPL2.0
+# description: ftrace - stacktrace filter command
+# flags: instance
+
+echo _do_fork:stacktrace >> set_ftrace_filter
+
+grep -q "_do_fork:stacktrace:unlimited" set_ftrace_filter
+
+(echo "forked"; sleep 1)
+
+grep -q "<stack trace>" trace