fix(unit tests): test_udp_syslog can overflow default size receive buffer

[strophy]

Summary

test_udp_syslog sends out 1000 UDP datagrams with no delay, which can saturate the kernel UDP receive buffer, depending on the environment. Specifically in Alpine Linux CI, this test was causing consistent failures. The test failure looks like this:

  TRY 4 FAIL [   2.192s] (2650/2654) vector sources::syslog::test::test_udp_syslog
  stdout ───
    running 1 test
    test sources::syslog::test::test_udp_syslog ... FAILED
    failures:
    failures:
        sources::syslog::test::test_udp_syslog
    test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 1834 filtered out; finished in 2.18s
  stderr ───
    thread 'sources::syslog::test::test_udp_syslog' (46526) panicked at src/sources/syslog.rs:1253:13:
    assertion `left == right` failed
      left: 917
     right: 1000
    note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

This PR specifies receive_buffer_bytes of 4MB which should be sufficient for the amount of data sent in the test, which I estimate to be around 500KB. This is typically doubled for overhead/padding, and then I added more headroom just to make sure, since this buffer sizing only applies during this specific test.

Vector configuration

Build from source, then:

	cargo nextest run \
		--fail-fast \
		--frozen \
		--no-default-features \
		--features default-musl,component-validation-runner \
		--offline \
		--release \
		--workspace \
		--test-threads num-cpus

How did you test this PR?

In Alpine Linux CI, test passes on x86_64, aarch64, ppc64le and riscv64

Change Type

• Bug fix
• New feature
• Dependencies
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the no-changelog label to this PR.

References

• Closes: Alpine packages #2886 (comment)
• Related: https://gitlab.alpinelinux.org/alpine/aports/-/merge_requests/92645

Notes

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[github-actions]

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[strophy]

I have read the CLA Document and I hereby sign the CLA

[pront]

Hi @strophy, thanks, I will merge this tomorrow.