We can't mount sysfs as rootless unless we manage the network
namespace. Problem: slirp4netns is now creating and managing a
network namespace separate from the OCI runtime, so we can't
mount sysfs in many circumstances. The `crun` OCI runtime will
automatically handle this by falling back to a bind mount, but
`runc` will not, so we didn't notice until RHEL gating tests ran
on the new branch.
Signed-off-by: Matthew Heon <mheon@redhat.com>