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/modern-go/reflect2/go_below_19.go

@@ -0,0 +1,14 @@
+//+build !go1.9
+
+package reflect2
+
+import (
+	"unsafe"
+)
+
+//go:linkname makemap reflect.makemap
+func makemap(rtype unsafe.Pointer) (m unsafe.Pointer)
+
+func makeMapWithSize(rtype unsafe.Pointer, cap int) unsafe.Pointer {
+	return makemap(rtype)
+}