Enable SYSTEM_DEFAULTS decap_qos_map via golden config

[markx-arista]

Description of PR

Summary:
Arista-7060X6-64PE-B-C448O16/C512S2 use generate_port_qos_map_per_sku in qos.json.j2, which prevents the global dscp_to_tc_map from being set in config_db.json. Without it, Broadcom ipinip decap falls through to SAI's built-in default instead of the intended decap_dscp_to_tc_map from ipinip.json.

Setting SYSTEM_DEFAULTS decap_qos_map status to 'enabled' lets ipinip.json.j2 use the SYSTEM_DEFAULTS attribute instead of hardcoded platform checks.
Fixes # (issue)

Type of change

• Bug fix
• Testbed and Framework(new/improvement)
• New Test case
  • Skipped for non-supported platforms
• Test case improvement

Back port request

• 202311
• 202405
• 202411
• 202505
• 202511
• 202512
• 202605

Tracking issue/work item for backport/cherry-pick request (GitHub issue or Microsoft ADO):
Failure type:

Tested branch

• master
• 202311
• 202405
• 202411
• 202505
• 202511
• 202512
• 202605
• N/A

Test result

With golden config enabling decap_qos_map:

admin@qspf201:~$ sonic-cfggen -d -v "SYSTEM_DEFAULTS"
{'decap_qos_map': {'status': 'enabled'}, 'mux_tunnel_egress_acl': {'status': 'disabled'}}

admin@qspf201:~$ sonic-db-cli APPL_DB HGETALL "TUNNEL_DECAP_TABLE:IPINIP_TUNNEL"
{'decap_dscp_to_tc_map': 'AZURE', 'dscp_mode': 'uniform', 'ecn_mode': 'copy_from_outer', 'ttl_mode': 'pipe', 'tunnel_type': 'IPINIP'}

admin@qspf201:~$ sonic-db-cli APPL_DB HGETALL "TUNNEL_DECAP_TABLE:IPINIP_V6_TUNNEL"
{'decap_dscp_to_tc_map': 'AZURE', 'dscp_mode': 'uniform', 'ecn_mode': 'copy_from_outer', 'ttl_mode': 'pipe', 'tunnel_type': 'IPINIP'}

Approach

What is the motivation for this PR?

Currently ipinip.json.j2 is having platform checks for enabling/disabling decap entries. We want to prevent having platform checks for simple enable/disable scenarios.

How did you do it?

SYSTEM_DEFAULTS['decap_qos_map']['status'] is added in sonic-net/sonic-buildimage#28588, and enable it for Arista-7060X6-64PE-B-C448O16/C512S2 in sonic-mgmt generate_golden_config_db.py.

How did you verify/test it?

Check config generated from the golden config and ipinip.json

Any platform specific information?

Supported testbed topology if it's a new test case?

Documentation

[mssonicbld]

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[mssonicbld]

This PR has backport request for branch(es): 202511,202605.
Added label(s) for branch(es) 202511,202605.

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[mssonicbld]

This PR has backport request label(s) for branch(es): 202511,202605, but is missing required test information. Please make sure you tick the tested branch(es) in the Tested branch section and provide test evidence (e.g., 202511: <test result>) in the Test result section as well in your PR description.

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