TUN-1615: revert miekg/dns to last known working revision

The last known good commit is 6da3249dfb57fbaa16efafcd8744cee8809d80cd before the first release tag.

vendor/golang.org/x/net/ipv4/sys_bpf.go

@@ -1,23 +0,0 @@
-// Copyright 2017 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build linux
-
-package ipv4
-
-import (
-	"unsafe"
-
-	"golang.org/x/net/bpf"
-	"golang.org/x/net/internal/socket"
-)
-
-func (so *sockOpt) setAttachFilter(c *socket.Conn, f []bpf.RawInstruction) error {
-	prog := sockFProg{
-		Len:    uint16(len(f)),
-		Filter: (*sockFilter)(unsafe.Pointer(&f[0])),
-	}
-	b := (*[sizeofSockFprog]byte)(unsafe.Pointer(&prog))[:sizeofSockFprog]
-	return so.Set(c, b)
-}