eBPF unit test: Remove expired codes & Add framework doc

[sancppp]

What type of PR is this?

/kind enhancement

What this PR does / why we need it:

Which issue(s) this PR fixes:
Fixes #1209

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

[Copilot]

Pull Request Overview

This PR removes outdated eBPF unit test code and adds documentation for the new eBPF unit test framework.

• Removed several expired test files (xdp_test.c, run_tests.sh, common.h, Makefile)
• Added comprehensive framework documentation in docs/ebpf_unit_test_zh.md

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
test/unittest/workload/xdp_test.c	Removed expired unit test implementation
test/unittest/workload/run_tests.sh	Removed outdated test runner script
test/unittest/workload/common.h	Removed unused header definitions and test macros
test/unittest/workload/Makefile	Removed obsolete build instructions for unit tests
docs/ebpf_unit_test_zh.md	Added documentation outlining the new testing framework

Comments suppressed due to low confidence (2)

docs/ebpf_unit_test_zh.md:1

• Consider including explicit instructions on how to run the new eBPF unit tests (e.g., command examples or integration details with the CI pipeline) to help users transition from the removed Makefile-based approach.

# Kmesh eBPF 单元测试框架文档

test/unittest/workload/xdp_test.c:1

• Since the expired test files are being removed, please ensure that any necessary tests have been migrated to the new framework to avoid any gaps in test coverage.

#include <errno.h>

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 46.21%. Comparing base (579f10b) to head (8ec0436).
Report is 56 commits behind head on main.

see 2 files with indirect coverage changes

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[LiZhenCheng9527]

/lgtm
/approve

[kmesh-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: LiZhenCheng9527

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