pw_transfer: Test recent service improvements
pw_transfer: Test recent service improvements

- Test that new transfers are not started when non-initial packets are
  received.
- Test that only a single transfer parameters update is sent after a
  drop in a write transfer.

Change-Id: I1dad6b2f5af7e9e00d753bda08a43a8cbeccb98d
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/63642
Commit-Queue: Wyatt Hepler <cca3bedb37979eacd157a9bceb473582df8aea1e@google.com>
Pigweed-Auto-Submit: Wyatt Hepler <cca3bedb37979eacd157a9bceb473582df8aea1e@google.com>
Reviewed-by: Keir Mierle <69344103cc60b36d6e1fbdc31ce6504b2286c646@google.com>

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed