Manifest: disable always-on VPN

We don't actually comprehend how this works yet, so disable it. But
we'll need to add support for this at some point.

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

app/src/main/AndroidManifest.xml

@@ -61,6 +61,8 @@
             <intent-filter>
                 <action android:name="android.net.VpnService" />
             </intent-filter>
+            <meta-data android:name="android.net.VpnService.SUPPORTS_ALWAYS_ON"
+                android:value="false" />
         </service>
 
         <service