ToolsInstaller: restrict to only main app usage

We don't want lots of different packages fighting over who gets to
install the tools.

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

app/src/main/java/com/wireguard/android/util/ToolsInstaller.java

@@ -105,6 +105,8 @@ public final class ToolsInstaller {
     }
 
     public int install() throws RootShellException, IOException {
+        if (!context.getPackageName().startsWith("com.wireguard."))
+            throw new SecurityException("The tools may only be installed system-wide from the main WireGuard app.");
         return willInstallAsMagiskModule() ? installMagisk() : installSystem();
     }