selinux: ignore unknown extended permissions

commit 900f83cf upstream.

When evaluating extended permissions, ignore unknown permissions instead
of calling BUG(). This commit ensures that future permissions can be
added without interfering with older kernels.

Cc: stable@vger.kernel.org
Fixes: fa1aa143 ("selinux: extended permissions for ioctls")
Signed-off-by: Thiébaud Weksteen <tweek@google.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Acked-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>