Propose `securityContext.sysMount: Unmasked` to Kubernetes

[AkihiroSuda]

It turned out that running rootlesskit --net=slirp4netns inside container requires unmasked sysfs, so as to mount sysfs with expected /sys/class/net entries.

#23 (comment)

[AkihiroSuda]

Docker (and Podman?) CLI is under discussion at docker/cli#1347