cablev2: only send one batch to AOA devices.

We already skipped splitting batches for caBLE devices, but AOA is a
different transport. But it needs the same accommodation.

BUG=1002262

Change-Id: I1dbe58516464ba1cd1294327b4b42f277e16e949
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2463810
Commit-Queue: Adam Langley <agl@chromium.org>
Reviewed-by: Martin Kreichgauer <martinkr@google.com>
Cr-Commit-Position: refs/heads/master@{#816797}