[fenix] Issue https://github.com/mozilla-mobile/fenix/issues/21437: Fix default of start_on_home setting in UI

app/src/main/res/xml/home_preferences.xml

@@ -38,7 +38,7 @@
         app:iconSpaceReserved="false">
 
         <org.mozilla.fenix.settings.RadioButtonPreference
-            android:defaultValue="true"
+            android:defaultValue="false"
             android:key="@string/pref_key_start_on_home_always"
             android:title="@string/opening_screen_homepage" />
 
@@ -48,7 +48,7 @@
             android:title="@string/opening_screen_last_tab" />
 
         <org.mozilla.fenix.settings.RadioButtonPreference
-            android:defaultValue="false"
+            android:defaultValue="true"
             android:key="@string/pref_key_start_on_home_after_four_hours"
             android:title="@string/opening_screen_after_four_hours_of_inactivity" />