Prefix on nicv6 support

[NihaNallappagari]

Reason for Change:
This PR has changes specific to Prefix on NICv6
CNS
--Consuming PrimaryIPv6, GatewayIPv6, MacAddress (DeletedNIC) from NNC CRD because of dualstack NC
--IP allocation: Assign IPs of each IPFamily as part of RequestIPs api request

IPAM
--Change RequestIPs response parsing to read GatewayIPv6 and MacAddress
--Populates Interfaces with MacAddress which is used by CNI to plumb routes to send traffic

Requirements:

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

Notes:

[Copilot]

Pull Request Overview

This PR introduces changes to support Prefix on NICv6 by enhancing CNS and IPAM components to handle dualstack IP allocation and additional interface information.

• Updated CNS to consume MACAddress from the network container request.
• Refactored IP assignment logic to support multiple IP families and enhanced error messages.
• Updated IP config response processing and CNI result construction to include and deduplicate gateway IPs and interface MAC addresses.

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
cns/restserver/util.go	Added MACAddress assignment to PodIpInfo to support NICv6 configuration.
cns/restserver/ipam.go	Refactored IP allocation logic to support dual IP families and introduced generateAssignedIPKey helper.
cns/restserver/internalapi_linux.go	Added IPv4 check to ensure SNAT rules are only applied to IPv4 addresses.
cns/kubecontroller/nodenetworkconfig/conversion_linux.go	Updated NC request conversion to handle IPv6 gateway and MACAddress assignment.
cns/NetworkContainerContract.go	Added GatewayIPv6Address field and IPFamily enum definitions.
azure-ipam/ipconfig/ipconfig.go	Modified ProcessIPConfigsResp to parse and return gateway IPs for both IPv4 and IPv6.
azure-ipam/ipam.go	Updated CNI result construction to include gateway IPs and deduplicate interface MAC addresses.

Comments suppressed due to low confidence (1)

cns/restserver/ipam.go:1028

• [nitpick] Consider renaming 'numberOfIPs' to a more descriptive name such as 'requiredIPCount' to clarify that it represents the count based on IP families rather than just the number of NCs.

if numOfIPFamilies != 0 {
			numberOfIPs = numOfIPFamilies
		}

[Copilot]

[nitpick] Consider adding logging or error handling when gateway IP parsing fails so that missing or invalid gateway IPs can be diagnosed more easily.

Suggested change

	if gatewayIP != nil {
	if gatewayIP == nil {
	fmt.Printf("Warning: Failed to parse gateway IP for PodIPInfo[%d]\n", i)
	} else {

[NihaNallappagari]

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