A switch can't override switch group values using default switch group values

[nqb]

Describe the bug
When a switch is member of a switch group, it's not possible to override switch group values using values defined in default switch group.

To Reproduce
Steps to reproduce the behavior:

1. Create a switch group with two settings different than default switch group:

[group swgroup]
description=swgroup desc
always_trigger=1
type=Hostapd
registrationVlan=50

2. Create a switch member of this group:

[10.10.10.1]
description=sw
group=swgroup

3. Override registrationVlan setting on switch with value of 5

=> switches.conf is updated with registrationVlan=5

4. Set registrationVlan setting to 2 (default value in default switch group)

=> switches.conf is updated but registrationVlan setting is not present in [10.10.10.1] section

5. Refresh your web page

=> change is gone

Expected behavior
registrationVlan=2 should be present in [10.10.10.1] section because it's a setting different from the switch group.

Additional context
Has been noticed on 10.1.0