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/netlink.go

@@ -0,0 +1,39 @@
+// Package netlink provides a simple library for netlink. Netlink is
+// the interface a user-space program in linux uses to communicate with
+// the kernel. It can be used to add and remove interfaces, set up ip
+// addresses and routes, and confiugre ipsec. Netlink communication
+// requires elevated privileges, so in most cases this code needs to
+// be run as root. The low level primitives for netlink are contained
+// in the nl subpackage. This package attempts to provide a high-level
+// interface that is loosly modeled on the iproute2 cli.
+package netlink
+
+import (
+	"errors"
+	"net"
+)
+
+var (
+	// ErrNotImplemented is returned when a requested feature is not implemented.
+	ErrNotImplemented = errors.New("not implemented")
+)
+
+// ParseIPNet parses a string in ip/net format and returns a net.IPNet.
+// This is valuable because addresses in netlink are often IPNets and
+// ParseCIDR returns an IPNet with the IP part set to the base IP of the
+// range.
+func ParseIPNet(s string) (*net.IPNet, error) {
+	ip, ipNet, err := net.ParseCIDR(s)
+	if err != nil {
+		return nil, err
+	}
+	return &net.IPNet{IP: ip, Mask: ipNet.Mask}, nil
+}
+
+// NewIPNet generates an IPNet from an ip address using a netmask of 32 or 128.
+func NewIPNet(ip net.IP) *net.IPNet {
+	if ip.To4() != nil {
+		return &net.IPNet{IP: ip, Mask: net.CIDRMask(32, 32)}
+	}
+	return &net.IPNet{IP: ip, Mask: net.CIDRMask(128, 128)}
+}