enable dual NIC support in transparent VLAN

[mugeshsp]

Reason for Change:
Enables dual NIC feature support in Azure Container Networking by adding the ability to skip default routes and improving ARP proxy configuration for transparent VLAN clients. This enhancement allows for better network isolation and custom routing scenarios in multi-interface container environments.

Requirements:

• [x ] uses conventional commit messages
• includes documentation
• adds unit tests
• relevant PR labels added

Notes:
This PR includes three main commits:

1. Added SkipDefaultRoutes field to network container request/response contracts
2. Implemented ARP proxy setting and custom subnet route addition for VLAN interfaces

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[Copilot]

Pull Request Overview

This PR enables dual NIC support in transparent VLAN by adding the ability to skip default routes and improving ARP proxy configuration for transparent VLAN clients. This enhancement allows for better network isolation and custom routing scenarios in multi-interface container environments.

• Added SkipDefaultRoutes field to network container request/response contracts
• Implemented ARP proxy setting and custom subnet route addition for VLAN interfaces
• Enabled dual NIC feature support on Linux platform

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
network/transparent_vlan_endpointclient_linux.go	Added ARP proxy configuration and custom routing logic with SkipDefaultRoutes support
cns/restserver/util.go	Propagated SkipDefaultRoutes field in network container responses and IP configuration
cns/NetworkContainerContract.go	Added SkipDefaultRoutes field to request/response contracts and updated string representation
cni/network/network_linux.go	Enabled dual NIC feature support for Linux platform
cni/network/multitenancy.go	Added SkipDefaultRoutes field to interface info configuration

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[Copilot]

Using shell command execution with string formatting could be vulnerable to command injection if ifName contains malicious characters. Consider using a safer approach or validating the interface name against a whitelist of allowed characters.

[Copilot]

Error values from net.ParseCIDR are being ignored. These parsing operations could fail and should be handled to prevent potential runtime panics or incorrect network configuration.

Suggested change

	gWIP, gwNet, _ := net.ParseCIDR(gatewayIP.String() + "/32")
	gWIP, gwNet, err := net.ParseCIDR(gatewayIP.String() + "/32")
	if err != nil {
	return errors.Wrapf(err, "failed to parse CIDR for gatewayIP %s", gatewayIP.String())
	}

[Copilot]

Error values from net.ParseCIDR are being ignored. These parsing operations could fail and should be handled to prevent potential runtime panics or incorrect network configuration.

Suggested change

	subnetPrefix, subnetIPNet, _ := net.ParseCIDR(subnetCIDR.String())
	subnetPrefix, subnetIPNet, err := net.ParseCIDR(subnetCIDR.String())
	if err != nil {
	return fmt.Errorf("failed to parse subnetCIDR %q: %w", subnetCIDR.String(), err)
	}

[Copilot]

This comment indicates uncertainty about the API design. Either clarify the difference or remove the comment if it's not actionable.