'Load Defaults' button does not discard offloading modes for interfaces.

[Alexey. Kalashnikov]

'Load Defaults' button does not discard offloading modes for edited interfaces.
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Steps to reproduce:
1. Deploy Fuel Master Node
2. Create new cluster with 5 slaves(controller, compute and cinder). Use Neutron with VLAN segmentation with 5 NIC architecture.
3. Select tab page "Networks", select Settings "Other" at "Public network assignment" check [Assign public network to all nodes] and click [Save Settings]
4. Select tab page "Nodes", check [Select All] and click [Configure interfaces]
5. For interface enp0s5 (Management) click on Offloading Modes: [Default] check "Enabled" for 'rx-all' and 'rx-vlan-offload'
6. For interface enp0s6 (Private) click on Offloading Modes: [Default] check "Disabled" for 'generic-receive-offload', 'generic-segmentation-offload', 'tcp-segmentation-offload'
7. Click [Apply]
8. Click [Load Defaults]

Expected result:
all edited interface settings were discarded to defaults
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Actual result:
Edited offloading modes were not discarded
See attached picture

[Julia Aranovich (jkirnosova)]

The issue should be fixed in Nailgun: after saving custom data by clicking Apply Changes (PUT /api/nodes/node_id/interfaces) Load Defaults (GET /api/nodes/node_id/interfaces/default_assignment) becomes to response with this particular saved data and not default values.