selftests: pidfd: add CONFIG_CHECKPOINT_RESTORE=y to config

kcmp syscall is used in pidfd_getfd_test.c, so add
CONFIG_CHECKPOINT_RESTORE=y to config to ensure kcmp is available.
Signed-off-by: Tommi Rantala <tommi.t.rantala@nokia.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/pidfd/config

@@ -4,3 +4,4 @@ CONFIG_USER_NS=y
 CONFIG_PID_NS=y
 CONFIG_NET_NS=y
 CONFIG_CGROUPS=y
+CONFIG_CHECKPOINT_RESTORE=y