ref_tracker: use %p instead of %px in debugfs dentry name

As Kees points out, this is a kernel address leak, and debugging is
not a sufficiently good reason to expose the real kernel address.

Fixes: 65b584f ("ref_tracker: automatically register a file in debugfs for a ref_tracker_dir")
Reported-by: Kees Cook <kees@kernel.org>
Closes: https://lore.kernel.org/netdev/202507301603.62E553F93@keescook/
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: jtlayton

lib/ref_tracker.c

@@ -434,7 +434,7 @@ void ref_tracker_dir_debugfs(struct ref_tracker_dir *dir)
 	if (dentry && !xa_is_err(dentry))
 		return;
 
-	ret = snprintf(name, sizeof(name), "%s@%px", dir->class, dir);
+	ret = snprintf(name, sizeof(name), "%s@%p", dir->class, dir);
 	name[sizeof(name) - 1] = '\0';
 
 	if (ret < sizeof(name)) {