Revert "Use netlink.SetPromiscOn instead of iproute2 command"

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

@@ -1,14 +0,0 @@
-package netlink
-
-// ideally golang.org/x/sys/unix would define IfReq but it only has
-// IFNAMSIZ, hence this minimalistic implementation
-const (
-	SizeOfIfReq = 40
-	IFNAMSIZ    = 16
-)
-
-type ifReq struct {
-	Name  [IFNAMSIZ]byte
-	Flags uint16
-	pad   [SizeOfIfReq - IFNAMSIZ - 2]byte
-}