set singleInstance to MainActivity

app/src/main/AndroidManifest.xml

@@ -126,14 +126,13 @@
 
         <activity
             android:name="com.geeksville.mesh.MainActivity"
-            android:label="@string/app_name"
+            android:launchMode="singleInstance"
             android:screenOrientation="portrait"
             android:windowSoftInputMode="stateAlwaysHidden"
             android:theme="@style/Theme.App.Starting"
             android:exported="true">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
-
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>