Description of problem:
Can't change default gateway of a static IPv4 address

We have a new rgegression when trying to change network default gateway of a static IPv4 address

Desired state: {'interfaces': [{'name': 'ens4f1', 'state': 'up', 'mtu': 150
0, 'ipv4': {'enabled': False}, 'ipv6': {'enabled': False}}, {'name': 'net_tes1', 'type': 'linux-bridge', 'state': 'up', 'mtu': 1500, 'bridge': {'port': [{'name': 'ens4f1'}
], 'options': {'stp': {'enabled': False}}}, 'ipv4': {'enabled': True, 'address': [{'ip': '5.5.5.5', 'prefix-length': 24}], 'dhcp': False}, 'ipv6': {'enabled': False}}, {'n
ame': 'ovirtmgmt'}], 'routes': {'config': [{'next-hop-address': '5.5.6.254', 'next-hop-interface': 'net_tes1', 'destination': '0.0.0.0/0', 'state': 'absent', 'table-id': 0
}, {'next-hop-address': '5.5.5.254', 'next-hop-interface': 'net_tes1', 'destination': '0.0.0.0/0', 'state': 'absent', 'table-id': 0}]}}

Version-Release number of selected component (if applicable):
rhvm-4.4.0-0.31.master.el8ev.noarch
nmstate-0.2.6-6.el8.noarch
vdsm-4.40.11-1.el8ev.x86_64
NetworkManager-1.22.8-4.el8.x86_64

How reproducible:
100%

Steps to Reproduce:
1. Attach network to host and set static IPv4 address, netmask and gateway
5.5.5.5
24
5.5.5.254
2. Edit the network and change the default gateway to 5.5.6.254 

Actual results:
Network is out-of-sync and the change doesn't apply on the host, it lost in the way. In the desired state we can see that the change is sent, but not applied on the host. 

Expected results:
Should work as expected