[bug] Property name of VXLAN interface

Describe the bug
The required property "name" of a VXLAN interface renders to "ifname" in the OpenWRT configuration, which causes luci to convert it to "device".

Steps To Reproduce
Steps to reproduce the behavior:

1. Go to 'Templates'
2. Click on '+ Add template'
3. Scroll down to 'Configuration Menu'
4. Check checkbox 'Interfaces'
5. Click 'Add Interface'
6. Choose type 'VXLAN' and fill in required information
7. Save and assign to a device
8. Open luci on selected device
9. Navigate to Network --> Interfaces
10. See the following error:

The existing network configuration needs to be changed for LuCI to function properly.

Upon pressing "Continue", ifname options will get renamed and the network will be restarted to apply the updated configuration. 

Expected behavior
It would be better to render directly to 'device' and not to 'ifname'.

Screenshots
If applicable, add screenshots to help explain your problem.

System Information:

• OS: [Debian 12]
• Python Version: [Python 3.11.2]
• OpenWISP 25.10.0

Start by tracing the VXLAN interface rendering path in the Python library and checking whether regression tests cover the generated OpenWrt configuration. Compare the rendered property with the expected device property, then add coverage showing that VXLAN interfaces no longer produce ifname and run the relevant test suite.