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/nl/addr_linux.go

@@ -0,0 +1,76 @@
+package nl
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+type IfAddrmsg struct {
+	syscall.IfAddrmsg
+}
+
+func NewIfAddrmsg(family int) *IfAddrmsg {
+	return &IfAddrmsg{
+		IfAddrmsg: syscall.IfAddrmsg{
+			Family: uint8(family),
+		},
+	}
+}
+
+// struct ifaddrmsg {
+//   __u8    ifa_family;
+//   __u8    ifa_prefixlen;  /* The prefix length    */
+//   __u8    ifa_flags;  /* Flags      */
+//   __u8    ifa_scope;  /* Address scope    */
+//   __u32   ifa_index;  /* Link index     */
+// };
+
+// type IfAddrmsg struct {
+// 	Family    uint8
+// 	Prefixlen uint8
+// 	Flags     uint8
+// 	Scope     uint8
+// 	Index     uint32
+// }
+// SizeofIfAddrmsg     = 0x8
+
+func DeserializeIfAddrmsg(b []byte) *IfAddrmsg {
+	return (*IfAddrmsg)(unsafe.Pointer(&b[0:syscall.SizeofIfAddrmsg][0]))
+}
+
+func (msg *IfAddrmsg) Serialize() []byte {
+	return (*(*[syscall.SizeofIfAddrmsg]byte)(unsafe.Pointer(msg)))[:]
+}
+
+func (msg *IfAddrmsg) Len() int {
+	return syscall.SizeofIfAddrmsg
+}
+
+// struct ifa_cacheinfo {
+// 	__u32	ifa_prefered;
+// 	__u32	ifa_valid;
+// 	__u32	cstamp; /* created timestamp, hundredths of seconds */
+// 	__u32	tstamp; /* updated timestamp, hundredths of seconds */
+// };
+
+const IFA_CACHEINFO = 6
+const SizeofIfaCacheInfo = 0x10
+
+type IfaCacheInfo struct {
+	IfaPrefered uint32
+	IfaValid    uint32
+	Cstamp      uint32
+	Tstamp      uint32
+}
+
+func (msg *IfaCacheInfo) Len() int {
+	return SizeofIfaCacheInfo
+}
+
+func DeserializeIfaCacheInfo(b []byte) *IfaCacheInfo {
+	return (*IfaCacheInfo)(unsafe.Pointer(&b[0:SizeofIfaCacheInfo][0]))
+}
+
+func (msg *IfaCacheInfo) Serialize() []byte {
+	return (*(*[SizeofIfaCacheInfo]byte)(unsafe.Pointer(msg)))[:]
+}