Refine TetherSettings

- Move TetherSettings to network/tether folder

- Refine unit tests

Bug: 237273138
Test: manual test
make RunSettingsRoboTests ROBOTEST_FILTER=TetherSettingsTest

Change-Id: I1eb79780df824c575e79047bdeb3a9276f061fe9
diff --git a/AndroidManifest.xml b/AndroidManifest.xml
index 5352562..0890048 100644
--- a/AndroidManifest.xml
+++ b/AndroidManifest.xml
@@ -760,7 +760,7 @@
                 <category android:name="android.intent.category.VOICE_LAUNCH" />
             </intent-filter>
             <meta-data android:name="com.android.settings.FRAGMENT_CLASS"
-                android:value="com.android.settings.TetherSettings" />
+                android:value="com.android.settings.network.tether.TetherSettings" />
             <meta-data android:name="com.android.settings.HIGHLIGHT_MENU_KEY"
                        android:value="@string/menu_key_network"/>
         </activity>
@@ -792,7 +792,7 @@
                   android:exported="true"
                   android:targetActivity="Settings$TetherSettingsActivity">
             <meta-data android:name="com.android.settings.FRAGMENT_CLASS"
-                android:value="com.android.settings.TetherSettings" />
+                android:value="com.android.settings.network.tether.TetherSettings" />
             <meta-data android:name="com.android.settings.HIGHLIGHT_MENU_KEY"
                        android:value="@string/menu_key_network"/>
         </activity-alias>