Read parameters for vpp host interface creation from config file

[ljkiraly]

Improvement details

Parameters of vpp init functions for host interface creation should be exposed.
If a configuration file is present, the parameter values should be read from this config.
If there is no configuration file the current parameter values should be used.
The parameter values of the api functions should be written into the configuration file.

Notes

Parameters and default values:

AF_PACKET:
    mode: 1 # - ethernet mode
    rxFrameSize: 10240
    txFrameSize: 10240
    rxFramesPerBlock: 1024
    txFramesPerBlock: 1024
    numRxQueues: 1
    numTxQueues: 0
    flags: 8 # - AF_PACKET v2 API
AF_XDP:
    mode: 0 # - auto mode
    rxqSize: 8192
    txqSize: 8192
    flags: 0

Configuration file path: /var/lib/networkservicemesh/vppapi-hostint-args.yaml

[denis-tingaikin]

Conceptually looks good. Added a few comments mostly related to style

[glazychev-art]

Is it possible to move this parameter to the NSM config?
I think it will be easier to see that vppinit can be configured

[ljkiraly]

Yes, eventually that was my initial approach. I can define this parameter as NSM config parameter and

1/ Pass it to init (Execute function) either changing argument list or using options pattern - each will change the function prototype and made reading/understanding the code harder. For example in main.go the call of this init function is complex already:
vppinit.Must(cfg.VppInit.Execute(ctx, vppConn, cfg.TunnelIP)),

Or
2/ Get the parameter value by os.Getenv() where I want to use the path name in apiparams.go: getConfig(...)

[ljkiraly]

@glazychev-art Going forward with 2nd alternative, detailed in comment above.