Description of problem:

When applying below config:

```
---
interfaces:
- name: eth1
  type: ethernet
  state: up
- name: br0
  type: linux-bridge
  state: up
  bridge:
    port:
        - name: eth1
  ipv4:
    dhcp: false
    enabled: false
  ipv6:
    autoconf: false
    dhcp: false
    enabled: true
```

The nmstate will get timeout error:

libnmstate.error.NmstateLibnmError: Unexpected failure of libnm when running the mainloop: run timeout

Version-Release number of selected component (if applicable):

nmstate-0.0.7-1.el8.src.rpm
NetworkManager-libnm-1.20.0-0.1.el8.x86_64

How reproducible:
100%

Steps to Reproduce:
1. sudo ip link add eth1 type veth peer name eth2
2. save above config to `1.yml` file.
3. sudo nmstate set 1.yml

Actual results:


Expected results:


Additional info:

Since link local address will be ignored, setting with link local address
has the same effect.

Root cause:

When autoconf and dhcp disabled for IPV6 with no ipv6 address assigned,
the br0 will be set as ipv6.method == link-local.


The NetworkManager try to wait the br0 for link up:

Jun 24 15:37:23 el8 NetworkManager[1011]: <info>  [1561361843.2431] device (br0): IPv6 config waiting until carrier is on

But at the stage of br0 activation, its slave profile is not created yet.