undo CL 92210044 / 5cb21eee2d35

<enter reason for undo>

««« original CL description
net: make use of SO_LINGER_SEC on darwin

Fixes #7971.

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/92210044
»»»

TBR=iant
R=golang-codereviews
CC=golang-codereviews
https://golang.org/cl/96220049

src/pkg/net/sockopt_posix.go

@@ -8,7 +8,6 @@ package net
 
 import (
 	"os"
-	"runtime"
 	"syscall"
 )
 
@@ -138,9 +137,5 @@ func setLinger(fd *netFD, sec int) error {
 		return err
 	}
 	defer fd.decref()
-	opt := syscall.SO_LINGER
-	if runtime.GOOS == "darwin" {
-		opt = syscall.SO_LINGER_SEC
-	}
-	return os.NewSyscallError("setsockopt", syscall.SetsockoptLinger(fd.sysfd, syscall.SOL_SOCKET, opt, &l))
+	return os.NewSyscallError("setsockopt", syscall.SetsockoptLinger(fd.sysfd, syscall.SOL_SOCKET, syscall.SO_LINGER, &l))
 }