net: fix TCP keepalive on dragonfly

Fixes #7528.

LGTM=jsing
R=jsing
CC=golang-codereviews
https://golang.org/cl/75140045

src/pkg/net/tcpsockopt_dragonfly.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.
+
+package net
+
+import (
+	"os"
+	"syscall"
+	"time"
+)
+
+// Set keep alive period.
+func setKeepAlivePeriod(fd *netFD, d time.Duration) error {
+	if err := fd.incref(); err != nil {
+		return err
+	}
+	defer fd.decref()
+
+	// The kernel expects milliseconds so round to next highest millisecond.
+	d += (time.Millisecond - time.Nanosecond)
+	msecs := int(time.Duration(d.Nanoseconds()) / time.Millisecond)
+
+	err := os.NewSyscallError("setsockopt", syscall.SetsockoptInt(fd.sysfd, syscall.IPPROTO_TCP, syscall.TCP_KEEPINTVL, msecs))
+	if err != nil {
+		return err
+	}
+	return os.NewSyscallError("setsockopt", syscall.SetsockoptInt(fd.sysfd, syscall.IPPROTO_TCP, syscall.TCP_KEEPIDLE, msecs))
+}

src/pkg/net/tcpsockopt_unix.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 dragonfly freebsd linux nacl netbsd
+// +build freebsd linux nacl netbsd
 
 package net