code review 12418043: net: add special netFD mutex

src/pkg/net/tcpsockopt_darwin.go

 // Copyright 2009 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.
 
 // TCP socket options for darwin
 
 package net
 
 import (
         "os"
         "syscall"
         "time"
 )
 
 // Set keep alive period.
 func setKeepAlivePeriod(fd *netFD, d time.Duration) error {
-        if err := fd.incref(false); err != nil {
+        if err := fd.incref(); err != nil {
                 return err
         }
         defer fd.decref()
 
         // The kernel expects seconds so round to next highest second.
         d += (time.Second - time.Nanosecond)
         secs := int(d.Seconds())
 
         return os.NewSyscallError("setsockopt", syscall.SetsockoptInt(fd.sysfd, syscall.IPPROTO_TCP, syscall.TCP_KEEPALIVE, secs))
 }