tunnel: do not keep service running when bringing tunnel down

Doing so causes the process to restart when the activity is cleared,
even when no tunnel is running. I fear this might also lead to the
current flurry of DeadSystemExceptions.

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

tunnel/src/main/java/com/wireguard/android/backend/GoBackend.java

@@ -324,6 +324,9 @@ public final class GoBackend implements Backend {
             currentTunnelHandle = -1;
             currentConfig = null;
             wgTurnOff(handleToClose);
+            try {
+                vpnService.get(0, TimeUnit.NANOSECONDS).stopSelf();
+            } catch (final TimeoutException ignored) { }
         }
 
         tunnel.onStateChange(state);