Add generic intrusive FIFO queue

We need several FIFO queues (a queue of packets, a queue of messages,
etc.).

Some of them are implemented using cbuf, a generic circular buffer. But
for recording, we need to store the packets in an unbounded queue until
they are written, so the queue was implemented manually.

Create a generic implementation (using macros) to avoid reimplementing
it every time.

app/tests/test_queue.c

@@ -0,0 +1,38 @@
+#include <assert.h>
+
+#include <queue.h>
+
+struct foo {
+    int value;
+    struct foo *next;
+};
+
+static void test_queue(void) {
+    struct my_queue QUEUE(struct foo) queue;
+    queue_init(&queue);
+
+    assert(queue_is_empty(&queue));
+
+    struct foo v1 = { .value = 42 };
+    struct foo v2 = { .value = 27 };
+
+    queue_push(&queue, next, &v1);
+    queue_push(&queue, next, &v2);
+
+    struct foo *foo;
+
+    assert(!queue_is_empty(&queue));
+    queue_take(&queue, next, &foo);
+    assert(foo->value == 42);
+
+    assert(!queue_is_empty(&queue));
+    queue_take(&queue, next, &foo);
+    assert(foo->value == 27);
+
+    assert(queue_is_empty(&queue));
+}
+
+int main(void) {
+    test_queue();
+    return 0;
+}