Some namespace path joining errors together with user ns

For example, we have started a container named test, and the init process' id is 14821.

1. [ipc] joining container test's ipc namespace together with user ns:

                "uidMappings": [{
                        "containerID": 0,
                        "hostID": 1000,
                        "size": 2000
                }],
                "gidMappings": [{
                        "containerID": 0,
                        "hostID": 1000,
                        "size": 2000
                }],
                "namespaces": [
                        {
                                "type": "ipc",
                                "path": "/proc/14821/ns/ipc"
                        },
                        {
                                "type": "user"
                        }
                ],

The result will be:

@lifubang ➜ ~/nstest $ sudo /workspaces/runc/runc run -d ipc
ERRO[0000] runc run failed: unable to start container process: error during container init: error mounting "mqueue" to rootfs at "/dev/mqueue": mount src=mqueue, dst=/dev/mqueue, dstFD=/proc/self/fd/8, flags=0xe: operation not permitted

2. I think joining the existing pid, net, and uts namespace path will have the same issue like ipc.

I don't know whether we should support this feature or not?

Reproduce the reported runc run -d ipc case using the shown user ID mappings and IPC namespace path, then compare it with joining the PID, network, and UTS namespace paths. Inspect the namespace setup and /dev/mqueue mount handling; done requires a decided and tested behavior for these namespace combinations.