runc update --resource missing pids-limit and l3-cache-schema

While runc update supports --pids-limit and --l3-cache-schema options, the --resources argument seems to miss them.

USAGE:
   runc update [command options] <container-id>

OPTIONS:
   --resources value, -r value  path to the file containing the resources to update or '-' to read from the standard input

The accepted format is as follow (unchanged values can be omitted):

{
  "memory": {
    "limit": 0,
    "reservation": 0,
    "swap": 0,
    "kernel": 0,
    "kernelTCP": 0
  },
  "cpu": {
    "shares": 0,
    "quota": 0,
    "period": 0,
    "realtimeRuntime": 0,
    "realtimePeriod": 0,
    "cpus": "",
    "mems": ""
  },
  "blockIO": {
    "weight": 0
  }
}

Note: if data is to be read from a file or the standard input, all
other options are ignored.

Although runc update -r does try to retrieve and set the pids limit, it is not shown in the example resource file contents. And currently l3-cache-schema cannot be set this way, which might be ok since it is not part of specs.LinuxResources.

Start at the runc update command's -r/--resources handling and compare its accepted resource format with the --pids-limit and --l3-cache-schema options. Verify how pids-limit is retrieved and applied, and determine whether l3-cache-schema should be supported despite not being part of specs.LinuxResources. Done means the documented input and actual behavior agree.