[doc]: Refactor netlink message for high frequency telemetry

[Pterosaur]

This pull request refines the documentation and sample code for transmitting IPFIX telemetry data over netlink messages. The changes clarify the netlink message structure, provide a visual breakdown, and update the kernel-side sample code to directly append IPFIX data as payload without extra netlink attributes.

Documentation improvements:

• Expanded the explanation of netlink message composition, detailing the netlink and genetlink headers and describing how IPFIX recordings are included as payload. Added a mermaid diagram to visually illustrate the message structure.

Sample code updates:

• Updated the kernel sample code to calculate the total IPFIX payload length, allocate the message buffer accordingly, and append IPFIX data directly to the payload, removing the use of netlink attributes and improving error handling.

[mssonicbld]

/azp run

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[mssonicbld]

/azp run

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[bandaru-viswanath]

packet-data ?

[Pterosaur]

Here is 'packet-beta' that is a flag of mermaid. https://docs.mermaidchart.com/mermaid-oss/syntax/packet.html

[mssonicbld]

/azp run

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