[Feature request] Joining a netns or create an ns connected to an interface

Wish a feature like firejail's :
```
--net=bridgename - enable network namespaces and connect to this bridge.
--net=ethernet_interface - enable network namespaces and connect to this
Ethernet interface.
--net=none - enable a new, unconnected network namespace.
--netns=name - Run the program in a named, persistent network namespace.

```
We able to choose a network namespace to join. Or create a network namespace with an interface connected/bridged to one specified interface.