Update preference text for Network & internet screen.

- Add footer info to Hotspot & tethering
- Add summary text for Data usage -> Network restrictions
- Update summary for Hotspot & tethering -> Portable Wi-Fi hotspot
- Remove quotes from Wi-Fi summary

Bug: 36296257
Test: make RunSettingsRoboTests

Change-Id: Ibab61b089521a3339e660e9df0db0cd1b316712b

src/com/android/settings/TetherSettings.java

@@ -132,6 +132,8 @@ public class TetherSettings extends RestrictedSettingsFragment
         super.onCreate(icicle);
 
         addPreferencesFromResource(R.xml.tether_prefs);
+        mFooterPreferenceMixin.createFooterPreference()
+            .setTitle(R.string.tethering_footer_info);
 
         mDataSaverBackend = new DataSaverBackend(getContext());
         mDataSaverEnabled = mDataSaverBackend.isDataSaverEnabled();