global: java access control has important semantic meaning

It's not right to blindly follow all of AndroidStudio's suggestions,
especially for things in tunnel/ which comprise useful API.

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

tunnel/src/main/java/com/wireguard/android/util/RootShell.java

@@ -177,7 +177,7 @@ public class RootShell {
         }
     }
 
-    private void stop() {
+    public void stop() {
         synchronized (lock) {
             if (process != null) {
                 process.destroy();