Skip automatic `if swapLimit == 0 { s.Linux.Resources.Memory.Swap = &limit }` when the swap controller is missing.
(default on Ubuntu 20.04)
Fix issue 7828 (regression in PR 7783 "cri: make swapping disabled with memory limit")
Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>