net: fix windows build

Ignore result of setting SO_BROADCAST.

Disable TestSimpleListenMulticastUDP as
setIPv4MulticastInterface is not implemented.

R=golang-dev, bradfitz, mikioh.mikioh
CC=golang-dev
https://golang.org/cl/5610044

src/pkg/net/multicast_test.go

@@ -86,7 +86,7 @@ func TestListenMulticastUDP(t *testing.T) {
 
 func TestSimpleListenMulticastUDP(t *testing.T) {
 	switch runtime.GOOS {
-	case "plan9":
+	case "plan9", "windows":
 		return
 	}
 

src/pkg/net/sockopt_windows.go

@@ -27,11 +27,7 @@ func setDefaultSockopts(s syscall.Handle, f, t int) error {
 	// to be handled by the correct socket.
 
 	// Allow broadcast.
-	err := syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_BROADCAST, 1)
-	if err != nil {
-		return os.NewSyscallError("setsockopt", err)
-	}
-
+	syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_BROADCAST, 1)
 	return nil
 }