Revert vendor directory to support old golang (GOPATH mode)

gomodule is still in progress to migrate for now, hence multus
team decide to keep vendor directory to support build without
gomodule.

vendor/github.com/vishvananda/netlink/bpf_linux.go

@@ -0,0 +1,62 @@
+package netlink
+
+/*
+#include <asm/types.h>
+#include <asm/unistd.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <unistd.h>
+
+static int load_simple_bpf(int prog_type, int ret) {
+#ifdef __NR_bpf
+	// { return ret; }
+	__u64 __attribute__((aligned(8))) insns[] = {
+		0x00000000000000b7ull | ((__u64)ret<<32),
+		0x0000000000000095ull,
+	};
+	__u8 __attribute__((aligned(8))) license[] = "ASL2";
+	// Copied from a header file since libc is notoriously slow to update.
+	// The call will succeed or fail and that will be our indication on
+	// whether or not it is supported.
+	struct {
+		__u32 prog_type;
+		__u32 insn_cnt;
+		__u64 insns;
+		__u64 license;
+		__u32 log_level;
+		__u32 log_size;
+		__u64 log_buf;
+		__u32 kern_version;
+	} __attribute__((aligned(8))) attr = {
+		.prog_type = prog_type,
+		.insn_cnt = 2,
+		.insns = (uintptr_t)&insns,
+		.license = (uintptr_t)&license,
+	};
+	return syscall(__NR_bpf, 5, &attr, sizeof(attr));
+#else
+	errno = EINVAL;
+	return -1;
+#endif
+}
+*/
+import "C"
+
+type BpfProgType C.int
+
+const (
+	BPF_PROG_TYPE_UNSPEC BpfProgType = iota
+	BPF_PROG_TYPE_SOCKET_FILTER
+	BPF_PROG_TYPE_KPROBE
+	BPF_PROG_TYPE_SCHED_CLS
+	BPF_PROG_TYPE_SCHED_ACT
+	BPF_PROG_TYPE_TRACEPOINT
+	BPF_PROG_TYPE_XDP
+)
+
+// loadSimpleBpf loads a trivial bpf program for testing purposes
+func loadSimpleBpf(progType BpfProgType, ret int) (int, error) {
+	fd, err := C.load_simple_bpf(C.int(progType), C.int(ret))
+	return int(fd), err
+}