wgengine/magicsock: move device close to uncursed portion of test.

Device close used to suffer from deadlocks, but no longer.

Signed-off-by: David Anderson <danderson@tailscale.com>

wgengine/magicsock/magicsock_test.go

@@ -389,6 +389,7 @@ func TestTwoDevicePing(t *testing.T) {
 	if err := dev1.Reconfig(&cfgs[0]); err != nil {
 		t.Fatal(err)
 	}
+	defer dev1.Close()
 
 	tun2 := tuntest.NewChannelTUN()
 	dev2 := device.NewDevice(tun2.TUN(), &device.DeviceOptions{
@@ -398,6 +399,7 @@ func TestTwoDevicePing(t *testing.T) {
 		SkipBindUpdate: true,
 	})
 	dev2.Up()
+	defer dev2.Close()
 
 	if err := dev2.Reconfig(&cfgs[1]); err != nil {
 		t.Fatal(err)
@@ -460,8 +462,6 @@ func TestTwoDevicePing(t *testing.T) {
 	if os.Getenv("RUN_CURSED_TESTS") == "" {
 		t.Skip("test is very broken, don't run in CI until it's reliable.")
 	}
-	defer dev1.Close() // TODO(crawshaw): this hangs
-	defer dev2.Close() // TODO(crawshaw): this hangs
 
 	pingSeq := func(t *testing.T, count int, totalTime time.Duration, strict bool) {
 		msg := func(i int) []byte {