ipn/ipnlocal: make TKA tests not have side effects

It left the envknob turned on which meant that running all the tests
in the package had different behavior than running just any one test.

Signed-off-by: Maisem Ali <maisem@tailscale.com>

ipn/ipnlocal/network-lock_test.go

@@ -67,6 +67,7 @@ func fakeNoiseServer(t *testing.T, handler http.HandlerFunc) (*httptest.Server,
 
 func TestTKAEnablementFlow(t *testing.T) {
 	envknob.Setenv("TAILSCALE_USE_WIP_CODE", "1")
+	defer envknob.Setenv("TAILSCALE_USE_WIP_CODE", "")
 	nodePriv := key.NewNode()
 
 	// Make a fake TKA authority, getting a usable genesis AUM which
@@ -149,6 +150,7 @@ func TestTKAEnablementFlow(t *testing.T) {
 
 func TestTKADisablementFlow(t *testing.T) {
 	envknob.Setenv("TAILSCALE_USE_WIP_CODE", "1")
+	defer envknob.Setenv("TAILSCALE_USE_WIP_CODE", "")
 	temp := t.TempDir()
 	os.Mkdir(filepath.Join(temp, "tka"), 0755)
 	nodePriv := key.NewNode()
@@ -265,6 +267,7 @@ func TestTKADisablementFlow(t *testing.T) {
 
 func TestTKASync(t *testing.T) {
 	envknob.Setenv("TAILSCALE_USE_WIP_CODE", "1")
+	defer envknob.Setenv("TAILSCALE_USE_WIP_CODE", "")
 
 	someKeyPriv := key.NewNLPrivate()
 	someKey := tka.Key{Kind: tka.Key25519, Public: someKeyPriv.Public().Verifier(), Votes: 1}
@@ -501,6 +504,7 @@ func TestTKASync(t *testing.T) {
 
 func TestTKAFilterNetmap(t *testing.T) {
 	envknob.Setenv("TAILSCALE_USE_WIP_CODE", "1")
+	defer envknob.Setenv("TAILSCALE_USE_WIP_CODE", "")
 
 	nlPriv := key.NewNLPrivate()
 	nlKey := tka.Key{Kind: tka.Key25519, Public: nlPriv.Public().Verifier(), Votes: 2}
@@ -559,6 +563,7 @@ func TestTKAFilterNetmap(t *testing.T) {
 
 func TestTKADisable(t *testing.T) {
 	envknob.Setenv("TAILSCALE_USE_WIP_CODE", "1")
+	defer envknob.Setenv("TAILSCALE_USE_WIP_CODE", "")
 	temp := t.TempDir()
 	os.Mkdir(filepath.Join(temp, "tka"), 0755)
 	nodePriv := key.NewNode()
@@ -647,6 +652,7 @@ func TestTKADisable(t *testing.T) {
 
 func TestTKASign(t *testing.T) {
 	envknob.Setenv("TAILSCALE_USE_WIP_CODE", "1")
+	defer envknob.Setenv("TAILSCALE_USE_WIP_CODE", "")
 	temp := t.TempDir()
 	os.Mkdir(filepath.Join(temp, "tka"), 0755)
 	nodePriv := key.NewNode()