[tests] Improve statsd performance benchmark on MacOS platforms

[sgnn7]

What does this PR do?

Few issues were noticed when running the statsd benchmark on MacOS that needed fixing

Description of the Change

• Receive buffer of the socket is now increased to reasonable levels (32k from 4k)
• Packet count warning was moot since we may send multiple metrics per packet
• If statsd.flush method is available, call it when the threaded sender exits to ensure that we are accounting for all of the metrics in the results.

Alternate Designs

Possible Drawbacks

Verification Process

Run benchmark on MacOS with 10 threads via UDS and see the reduction in packet drops

Additional Notes

Release Notes

Review checklist (to be filled by reviewers)

• [ ] Feature or bug fix MUST have appropriate tests (unit, integration, etc...)
• [ ] PR title must be written as a CHANGELOG entry (see why)
• [ ] Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• [ ] PR must have one changelog/ label attached. If applicable it should have the backward-incompatible label attached.
• [ ] PR should not have do-not-merge/ label attached.
• [ ] If Applicable, issue must have kind/ and severity/ labels attached at least.