ipn: put e2e login section in its own subtest

Signed-off-by: David Crawshaw <crawshaw@tailscale.com>

ipn/e2e_test.go

@@ -68,6 +68,7 @@ func TestIPN(t *testing.T) {
 	defer n2.Backend.Shutdown()
 	n2.Backend.StartLoginInteractive()
 
+	t.Run("login", func(t *testing.T) {
 		var s1, s2 State
 		for {
 			t.Logf("\n\nn1.state=%v n2.state=%v\n\n", s1, s2)
@@ -105,6 +106,7 @@ func TestIPN(t *testing.T) {
 				t.Fatalf("\n\n\nFATAL: timed out waiting for notifications.\n\n\n")
 			}
 		}
+	})
 
 	n1addr := n1.Backend.NetMap().Addresses[0].IP
 	n2addr := n2.Backend.NetMap().Addresses[0].IP