WgQuickBackend: by default use single-tunnel mode like GoBackend, but add option

Note that this currently doesn't play well with people activating
wg-quick tunnels from outside the app. Those tunnels won't be
deactivated. But presumably that's desired behavior anyway, considering
people are mucking around at the command line.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

ui/src/main/java/com/wireguard/android/activity/SettingsActivity.java

@@ -99,7 +99,8 @@ public class SettingsActivity extends ThemeChangeAwareActivity {
 
             final Preference wgQuickOnlyPrefs[] = {
                     getPreferenceManager().findPreference("tools_installer"),
-                    getPreferenceManager().findPreference("restore_on_boot")
+                    getPreferenceManager().findPreference("restore_on_boot"),
+                    getPreferenceManager().findPreference("multiple_tunnels")
             };
             for (final Preference pref : wgQuickOnlyPrefs)
                 pref.setVisible(false);