Description of problem:
To reset vlan-filtering from a linux bridge it was possible to specify "vlan: {}" at the bridge port, this is no longer the case and it get merged with previous vlan config so it isn't reset.


Version-Release number of selected component (if applicable):
nmstate-1.0.2-18.el8.noarch

How reproducible:
Always


Steps to Reproduce:
1. Create a linux-bridge with vlan-filtering
nmstatectl apply << EOF
> interfaces:
>   - name: dummy1
>     type: dummy
>     state: up
>   - name: linux-br0
>     type: linux-bridge
>     state: up
>     bridge:
>       port:
>         - name: dummy1
>           stp-hairpin-mode: false
>           stp-path-cost: 100
>           stp-priority: 32
>           vlan:
>             mode: trunk
>             trunk-tags:
>               - id: 101
>               - id-range:
>                   min: 500
>                   max: 599
>             tag: 100
>             enable-native: true
> EOF

2. Reset the vlan-filtering at the bridge
nmstatectl apply << EOF
> interfaces:
>   - name: dummy1
>     type: dummy
>     state: up
>   - name: linux-br0
>     type: linux-bridge
>     state: up
>     bridge:
>       port:
>         - name: dummy1
>           stp-hairpin-mode: false
>           stp-path-cost: 100
>           stp-priority: 32
>           vlan: {}
> EOF


Actual results:
Vlan configuration is still there
The vlan configuration is still there
nmstatectl show linux-br0 |grep vlan -A 8
      vlan:
        enable-native: true
        mode: trunk
        tag: 100
        trunk-tags:
        - id: 101
        - id-range:
            max: 599
            min: 500



Expected results:
The vlan configuration should be gone


Additional info:
It was discover as part of https://github.com/nmstate/nmstate/pull/1830, it also found that there is a false possitive at the test_disable_vlan_filtering_on_bridge integration test