It isn't possible to setup networks for nodes in created node group

[Ilya Popov]

Steps to reproduce:

1. create new node group in fuel environment
2. setup network settings with vlan id for group created in step 1 (For public, storage,management, private networks, PXE will be untagged)
3. add node to network group from step 1
4. select node and click "interface configuration"

You will see "untagged networks cannot be assigned to the same interface" message

If your node have more than one network interface - you won't able to change default placement of networks for this interfaces.