Problem:
In check-config.sh assumptions are made about cgroups v1/v2/hybrid,
causes false-negative on pure V2 system.
Solution:
In check-config.sh implement the same validation as found in
./pkg/agent/run.go -> validate(), validateCgroupsV1(), validateCgroupsV2()
[ which use containerd/cgroups:utils.go -> Mode() ]
Signed-off-by: Rowan Thorpe <rowan@rowanthorpe.com>
If the ip_set kernel module is not available we should warn
that the network policy controller can not start rather than
cause a fatal error.
Also adds module probing and config checks for ip_set.
