Only display options to save and cancel edits to the displayed APN if the APN is editable.

Test: mp settingsg and look at the UI. This class does not yet have
tests.

Current design:
 - https://screenshot.googleplex.com/BgrLPsz3ebxBnMa
 - https://screenshot.googleplex.com/AeRQe6Rh8SxjjMw

Updated design: https://screenshot.googleplex.com/3bhmWwMjhEXh2Eu

Change-Id: Ic9794ca14534adde92a641560a00b1bd876d52cb

src/com/android/settings/network/apn/ApnEditor.java

@@ -805,8 +805,11 @@ public class ApnEditor extends SettingsPreferenceFragment
     @Override
     public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
         super.onCreateOptionsMenu(menu, inflater);
+        if (mReadOnlyApn) {
+            return;
+        }
         // If it's a new APN, then cancel will delete the new entry in onPause
-        if (!mNewApn && !mReadOnlyApn) {
+        if (!mNewApn) {
             menu.add(0, MENU_DELETE, 0, R.string.menu_delete)
                 .setIcon(R.drawable.ic_delete);
         }