net: fix build

https://golang.org/cl/16953 broke the world.

Change-Id: I7cbd4105338ff896bd0c8f69a0b126b6272be2e5
Reviewed-on: https://go-review.googlesource.com/17914Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/hook.go

@@ -4,11 +4,8 @@
 
 package net
 
-import "time"
-
 var (
 	testHookDialTCP      = dialTCP
-	testHookDNSDialer    = func(d time.Duration) dnsDialer { return &Dialer{Timeout: d} }
 	testHookHostsPath    = "/etc/hosts"
 	testHookLookupIP     = func(fn func(string) ([]IPAddr, error), host string) ([]IPAddr, error) { return fn(host) }
 	testHookSetKeepAlive = func() {}

src/net/hook_unix.go

@@ -6,10 +6,14 @@
 
 package net
 
-import "syscall"
+import (
+	"syscall"
+	"time"
+)
 
 var (
 	testHookDialChannel = func() {} // see golang.org/issue/5349
+	testHookDNSDialer   = func(d time.Duration) dnsDialer { return &Dialer{Timeout: d} }
 
 	// Placeholders for socket system calls.
 	socketFunc        func(int, int, int) (int, error)         = syscall.Socket