internal/socket: fix 386 emulation on amd64 for FreeBSD

Unlike routing messages, there's no need to tweak the alignment for
socket control messages on freebsd/386 emulation.

Change-Id: Iab4a2b05080868721f7e42cebd661d445f8c1030
Reviewed-on: https://go-review.googlesource.com/44391
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

internal/socket/sys_bsdvar.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build netbsd openbsd
+// +build freebsd netbsd openbsd
 
 package socket
 

internal/socket/sys_freebsd.go

-// 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.
-
-package socket
-
-import (
-	"syscall"
-	"unsafe"
-)
-
-func probeProtocolStack() int {
-	var p uintptr
-	align := int(unsafe.Sizeof(p))
-	// In the case of kern.supported_archs="amd64 i386", we need
-	// to know the underlying kernel's architecture because the
-	// alignment for socket facilities are set at the build time
-	// of the kernel.
-	conf, _ := syscall.Sysctl("kern.conftxt")
-	for i, j := 0, 0; j < len(conf); j++ {
-		if conf[j] != '\n' {
-			continue
-		}
-		s := conf[i:j]
-		i = j + 1
-		if len(s) > len("machine") && s[:len("machine")] == "machine" {
-			s = s[len("machine"):]
-			for k := 0; k < len(s); k++ {
-				if s[k] == ' ' || s[k] == '\t' {
-					s = s[1:]
-				}
-				break
-			}
-			if s == "amd64" {
-				align = 8
-			}
-			break
-		}
-	}
-	return align
-}