CHROMIUM: arcvm: Disable USER_NS

This patch disables user namespaces in arcvm. This is now required by
Android VTS on Android 13.

BUG=b:236909184
TEST=NetdNamespaceTest#CheckNoUserNamespaceSupport passes
(chroot) $ cros_workon --board=${BOARD} start arcvm-kernel-ack-5_10
(chroot) $ emerge-$BOARD arcvm-kernel-ack-5_10
(chroot) $ cros deploy <dut_ip> arcvm-kernel-ack-5_10
(tm-dev lunch terminal) $ atest netd_integration_test

Change-Id: Ie043e6c94f860081676e541629d11545f493e5fa
Signed-off-by: Hugo Benichi <hugobenichi@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/3833529


Reviewed-by: Sangwhan Moon <sxm@google.com>
Commit-Queue: Sangwhan Moon <sxm@google.com>
Reviewed-by: Cassie Wang <cassiewang@google.com>
Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Tested-by: Sangwhan Moon <sxm@google.com>
Signed-off-by: Richard Fung <richardfung@google.com>