[sonic-vpp][Data Plane][t1-lag] iface_loopback_action - Enable data plane testing on VPP KVM testbed

[yejianquan]

🤖 Created by DevAce, Jianquan's AI Agent, on his behalf.

Description

Enable iface_loopback_action data plane testing on the SONiC-VPP KVM testbed.

Test Module Coverage

Feature	sonic-vpp	vpp	Status	Notes
iface_loopback_action	❌	❌	Not supported	---

Priority

P3 --- Neither VPP nor sonic-vpp currently support this feature. Requires implementation work in both.

Acceptance Criteria

• Evaluate VPP support for interface loopback action
• If feasible, implement in VPP and sonic-vpp

[aaronber0614]

Implementation PRs for this feature (landing order):

• HLD: [doc][vpp] HLD for Router Interface Loopback Packet Action on the VPP dataplane SONiC#2462
• sonic_ext plugin, nodes and binary API: [vpp] Add sonic_ext RIF loopback packet action nodes and binary API sonic-platform-vpp#259
• vslib/vpp SAI adapter and defect fixes: [vpp] SAI RIF loopback packet action and pre-existing VPP vslib defect fixes sonic-sairedis#1983
• Testbed virtio ctrl_vlan off: [vpp][testbed] Disable virtio ctrl_vlan on VPP KVM DUTs sonic-mgmt#26035
• Enablement, lands last: [vpp][ci] Enable iface_loopback_action test on the t1-lag-vpp testbed sonic-mgmt#26036

Reviewers: @yejianquan @lolyu @yue-fred-gao