Description of problem:
When using ovs, an interface named 'ovs-system' will be generated automatically into sysfs. Now nmstate shows it if you run "nmstatectl show". In some scenarios it can cause a failure, such as using "nmstatectl edit" to change the configures, say change a bond ip, then :wq save and apply a global state, it will fail because of 'ovs-system' interface.

Version-Release number of selected component (if applicable):
NetworkManager-1.28.0-0.1.el8.x86_64
nispor-0.6.1-2.el8.x86_64
nmstate-0.4.1-1.el8.noarch
DISTRO=RHEL-8.4.0-20201028.d.1
Linux hp-dl388g8-04.rhts.eng.pek2.redhat.com 4.18.0-240.8.el8.x86_64 #1 SMP Sun Oct 25 16:56:23 EDT 2020 x86_64 x86_64 x86_64 GNU/Linux

How reproducible:
100%

Steps to Reproduce:
echo "---
interfaces:
- name: ovs-br0
  type: ovs-bridge
  state: up
  bridge:
    port:
    - name: ovs0" | nmstatectl set
nmstatectl show ovs-system
nmstatectl show | nmstatectl set

Actual results:
Failed

Expected results:
No failure

Additional info:
Traceback (most recent call last):
  File "/usr/bin/nmstatectl", line 11, in <module>
    load_entry_point('nmstate==0.4.1', 'console_scripts', 'nmstatectl')()
  File "/usr/lib/python3.6/site-packages/nmstatectl/nmstatectl.py", line 70, in main
    return args.func(args)
  File "/usr/lib/python3.6/site-packages/nmstatectl/nmstatectl.py", line 280, in apply
    args.save_to_disk,
  File "/usr/lib/python3.6/site-packages/nmstatectl/nmstatectl.py", line 309, in apply_state
    save_to_disk=save_to_disk,
  File "/usr/lib/python3.6/site-packages/libnmstate/netapplier.py", line 71, in apply
    _apply_ifaces_state(plugins, net_state, verify_change, save_to_disk)
  File "/usr/lib/python3.6/site-packages/libnmstate/netapplier.py", line 115, in _apply_ifaces_state
    _verify_change(plugins, net_state)
  File "/usr/lib/python3.6/site-packages/libnmstate/netapplier.py", line 120, in _verify_change
    net_state.verify(current_state)
  File "/usr/lib/python3.6/site-packages/libnmstate/net_state.py", line 63, in verify
    self._ifaces.verify(current_state.get(Interface.KEY))
  File "/usr/lib/python3.6/site-packages/libnmstate/ifaces/ifaces.py", line 405, in verify
    cur_iface.state_for_verify(),
libnmstate.error.NmstateVerificationError: 
desired
=======
---
name: ovs-system
type: ovs-interface
state: down
ipv4:
  enabled: false
  address: []
ipv6:
  enabled: false
  address: []
mac-address: 6A:C5:FB:85:09:98
mtu: 1500

current
=======
---
name: ovs-system
type: ovs-interface
state: down
ipv4:
  enabled: false
ipv6:
  enabled: false
mac-address: 6A:C5:FB:85:09:98
mtu: 1500

difference
==========
--- desired
+++ current
@@ -4,9 +4,7 @@
 state: down
 ipv4:
   enabled: false
-  address: []
 ipv6:
   enabled: false
-  address: []
 mac-address: 6A:C5:FB:85:09:98
 mtu: 1500