Add more XDP related blogs (#135)

* add setup

* update

* fix code

* move to dir

* fix code

* update the code

* update code of 42

* update 21

* update

* fix linter issues and add xdp in rust

* update the docker file

* fix CI

* fix kernel code

* update

* update

* add guidline

src/42-xdp-loadbalancer/no-docker/xdp_pass.c

@@ -0,0 +1,14 @@
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+
+SEC("xdp")
+int xdp_pass(struct xdp_md* ctx) {
+    void* data = (void*)(long)ctx->data;
+    void* data_end = (void*)(long)ctx->data_end;
+    int pkt_sz = data_end - data;
+
+    bpf_printk("packet size is %d", pkt_sz);
+    return XDP_PASS;
+}
+
+char __license[] SEC("license") = "GPL";