[swss] Support per-VLAN MAC learning disable

[thanushgowda123]

Summary

Implements per-VLAN MAC learning control in SONiC SWSS daemons:

• vlanmgr: Parses and propagates learn_disable from CONFIG_DB to APPL_DB
• portsorch: Programs SAI_VLAN_ATTR_LEARN_DISABLE via SAI API
• DVS Test: End-to-end regression test for complete pipeline

What Changed

cfgmgr/vlanmgr.cpp

• Reads learn_disable from CONFIG_DB VLAN events
• Forwards to APPL_DB VLAN_TABLE

orchagent/portsorch.cpp

• Reads learn_disable from APPL_DB
• Calls SAI: sai_vlan_api->set_vlan_attribute(vlan_oid, SAI_VLAN_ATTR_LEARN_DISABLE)

tests/test_vlan_mac_learning.py

• DVS regression test validating complete pipeline

Testing

Tested on:

• Single Switch Topology: Verified vlanmgr and portsorch functionality, SAI API calls confirmed in syslog
• Dual Switch + Trunk Topology: Validated multi-switch independence, cross-leaf traffic
• Leaf-Spine CLOS Fabric: Enterprise-scale validation with 3 leaves and 2 spines

Backward Compatibility

Fully backward compatible - default learning enabled, optional field

Related PRs

Part of a coordinated 3-PR feature submission:

• sonic-buildimage: Add learn_disable leaf to VLAN
• sonic-utilities: Add per-VLAN MAC learning control CLI commands

Merge order: buildimage #28861 → swss #4819 (this PR) → utilities #4747

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[mssonicbld]

/azp run

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[mssonicbld]

Hi, there are workflow run(s) waiting for approval, you may be first-time contributor. I will notify maintainers to help approve once PR is approved. Thanks!

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