feat: add use_primary_interface option to control IP detection behavior

[sungjinfcc]

This PR adds a new optional flag use_primary_interface to toggle between retrieving the VM IP from only the primary network interface (default behavior) or from any available interface via QEMU agent.

[Tinyblargon]

@sungjinfcc thank you for helping out with the project. There is however an issue with the feature you are trying to add:
It is adding a new setting that isn't very versatile, there are probably situations where a user wants to select the 3rd interface.

Would you be able and willing to make the following changes?

Rename the setting to primary_network?

Allow as input numbers and the id of the network interface.
Setting the id would use that interface as the primary.
Where as setting a number would pick the N th network inteface.

For example if you have the following interfaces: net0 net7 net12
And primary_network is 2 then it picks net12

[sungjinfcc]

@Tinyblargon thank you for the feedback. I've enhanced the feature to be more versatile while preserving all original functionality.

Enhanced primary_network setting:

• 0 (default): Use primary interface
• -1: Try all available interfaces
• N (positive): Use specific interface ID or Nth interface

Examples:

• primary_network = 7 → Use net7 (specific ID)
• primary_network = 2 → Use 2nd interface
• primary_network = -1 → Try all interfaces

[Tinyblargon]

@sungjinfcc Really like the edition of -1 as I understand it correctly it will go through the interfaces until it finds one with a valid IP.

I don't get the following example, how do we differentiate between 7th interface and net7 and between 2nd interface and net2?

primary_network = 7 → Use net7 (specific ID)
primary_network = 2 → Use 2nd interface

[sungjinfcc]

@Tinyblargon Yes, -1 will try all interfaces until it finds one with a valid IP

The logic prioritizes ID over position. For example, if VM has net0, net7, net12:

• primary_network = 7 → Uses net7 (ID match)
• primary_network = 2 → No net2 exists, uses 2nd interface (net7)
• primary_network = 12 → Uses net12 (ID match)