Update the description of ip-ttl and dscp

[tasaleh]

Update the description of the following leaves:

ip-ttl: Since this leave models both TTL (IPv4) and Hop Limit (IPv6) values, then, we need to indicate this explicitly in the leaf's description.

dscp: Update the description of the behavior when the leaf is not configured. When the leaf is not configured, the value of the inner packet will be copied over as the outer packet's value during encapsulation.

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[gemini-code-assist]

Code Review

This pull request updates the descriptions for the dscp and ip-ttl leaves in openconfig-aft-common.yang to clarify encapsulation behavior. The review feedback correctly identifies a syntax error in the dscp description caused by a curly double quote, as well as capitalization and spacing inconsistencies regarding 'Hop Limit' in the ip-ttl description.

[navaneethyv]

OC operator review July 14th.

Thanks for your contribution.

Can you add references to this in the PR description? Do we have an RFC that specifics this or 2 vendor implementations that support this behavior?

[navaneethyv]

OC review 28th.

Added a few comments, + requesting for supporting implementations from 2 vendors.

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https://github.com/openconfig/public/pull/1511/checks?check_run_id=87139774474