net: use internal/poll for DragonFly setKeepAlivePeriod

Fixes DragonFly build.

Change-Id: Id6b439cd4023ea8e3ed7cd9b70eec553c9eee4be
Reviewed-on: https://go-review.googlesource.com/36916
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/tcpsockopt_dragonfly.go

@@ -5,22 +5,20 @@
 package net
 
 import (
-	"os"
+	"runtime"
 	"syscall"
 	"time"
 )
 
 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(d / time.Millisecond)
-	if err := syscall.SetsockoptInt(fd.sysfd, syscall.IPPROTO_TCP, syscall.TCP_KEEPINTVL, msecs); err != nil {
-		return os.NewSyscallError("setsockopt", err)
+	if err := fd.pfd.SetsockoptInt(syscall.IPPROTO_TCP, syscall.TCP_KEEPINTVL, msecs); err != nil {
+		return wrapSyscallError("setsockopt", err)
 	}
-	return os.NewSyscallError("setsockopt", syscall.SetsockoptInt(fd.sysfd, syscall.IPPROTO_TCP, syscall.TCP_KEEPIDLE, msecs))
+	err := fd.pfd.SetsockoptInt(syscall.IPPROTO_TCP, syscall.TCP_KEEPIDLE, msecs)
+	runtime.KeepAlive(fd)
+	return wrapSyscallError("setsockopt", err)
 }