Demo app: Do not allow tunneling on API < 21

Without this patch, enabling tunneling on an API < 21 device
would result in an method not existing exception and the
app would crash.

PiperOrigin-RevId: 275428851

demos/main/src/main/java/com/google/android/exoplayer2/demo/PlayerActivity.java

@@ -206,7 +206,7 @@ public class PlayerActivity extends AppCompatActivity
       DefaultTrackSelector.ParametersBuilder builder =
           new DefaultTrackSelector.ParametersBuilder(/* context= */ this);
       boolean tunneling = intent.getBooleanExtra(TUNNELING, false);
-      if (tunneling) {
+      if (Util.SDK_INT >= 21 && tunneling) {
         builder.setTunnelingAudioSessionId(C.generateAudioSessionIdV21(/* context= */ this));
       }
       trackSelectorParameters = builder.build();

demos/main/src/main/java/com/google/android/exoplayer2/demo/SampleChooserActivity.java

@@ -127,6 +127,9 @@ public class SampleChooserActivity extends AppCompatActivity
     preferExtensionDecodersMenuItem.setVisible(useExtensionRenderers);
     randomAbrMenuItem = menu.findItem(R.id.random_abr);
     tunnelingMenuItem = menu.findItem(R.id.tunneling);
+    if (Util.SDK_INT < 21) {
+      tunnelingMenuItem.setEnabled(false);
+    }
     return true;
   }