benchmark: fix net-wrap-js-stream-passthrough

The net-wrap-js-stream-passthrough benchmark was inadvertently broken by 00944c7c. This fixes it.

👍 here to fast-track. This fixes node-daily-master Jenkins job. (The benchmark tests are only run there.)

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines