modules: rename packages/kernel_modules to packages/lkmc

Then inside, split packages/lkmc into kernel_modules and userland,
to keep userland out of the kernel_modules parent path, which makes no
sense.

Copy built modules and userland to the output rootfs overlay.

Document Linux distro tradeoffs.

packages/lkmc/kernel_modules/work_from_work.c

@@ -0,0 +1,40 @@
+/* https://github.com/cirosantilli/linux-kernel-module-cheat#workqueue-from-workqueue */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/workqueue.h>
+
+static int i;
+static struct workqueue_struct *queue;
+
+static void work_func(struct work_struct *work);
+
+DECLARE_DELAYED_WORK(next_work, work_func);
+DECLARE_WORK(work, work_func);
+
+static void work_func(struct work_struct *work)
+{
+	pr_info("%d\n", i);
+	i++;
+	if (i == 10)
+		i = 0;
+	queue_delayed_work(queue, &next_work, HZ);
+}
+
+static int myinit(void)
+{
+	queue = create_workqueue("myworkqueue");
+	queue_work(queue, &work);
+	return 0;
+}
+
+static void myexit(void)
+{
+	cancel_delayed_work(&next_work);
+	flush_workqueue(queue);
+	destroy_workqueue(queue);
+}
+
+module_init(myinit)
+module_exit(myexit)
+MODULE_LICENSE("GPL");