Avoid double-counting NIC throughput when VLAN interfaces exist

[engcurious]

Describe the enhancement

Cockpit currently shows network performance (throughput/speed) per network interface and also renders it in graphs.

When a physical NIC is split into multiple VLAN interfaces, Cockpit shows:

• Traffic for each VLAN interface
• Traffic for the underlying physical NIC

Because VLAN traffic is already carried by the physical NIC, this results in double-counting:

• The total network throughput appears inflated
• The performance graph shows a higher aggregate speed than the server is actually capable of

In practice, the sum of all VLAN interfaces equals the physical NIC traffic, so displaying both at the same time causes misleading results.

Which page, if applicable, is this related to?

None