net: make use of noDeadline instead of time.Time{}

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/11691044

src/pkg/net/dnsclient_unix.go

@@ -46,7 +46,7 @@ func exchange(cfg *dnsConfig, c Conn, name string, qtype uint16) (*dnsMsg, error
 		}
 
 		if cfg.timeout == 0 {
-			c.SetReadDeadline(time.Time{})
+			c.SetReadDeadline(noDeadline)
 		} else {
 			c.SetReadDeadline(time.Now().Add(time.Duration(cfg.timeout) * time.Second))
 		}

src/pkg/net/fd_posix_test.go

@@ -15,7 +15,7 @@ var deadlineSetTimeTests = []struct {
 	input    time.Time
 	expected int64
 }{
-	{time.Time{}, 0},
+	{noDeadline, 0},
 	{time.Date(2009, 11, 10, 23, 00, 00, 00, time.UTC), 1257894000000000000}, // 2009-11-10 23:00:00 +0000 UTC
 }
 
@@ -42,7 +42,7 @@ var deadlineExpiredTests = []struct {
 	// the start of TestDeadlineExpired
 	{time.Now().Add(5 * time.Minute), false},
 	{time.Now().Add(-5 * time.Minute), true},
-	{time.Time{}, false}, // no deadline set
+	{noDeadline, false},
 }
 
 func TestDeadlineExpired(t *testing.T) {

src/pkg/net/sock_posix.go

@@ -63,7 +63,7 @@ func socket(net string, f, t, p int, ipv6only bool, ulsa, ursa syscall.Sockaddr,
 		}
 		fd.isConnected = true
 		if !deadline.IsZero() {
-			setWriteDeadline(fd, time.Time{})
+			setWriteDeadline(fd, noDeadline)
 		}
 	}