Log Message:
The release notes for iperf 3.1.6 describe changes, including bug
fixes and new functionality, made since iperf 3.1.5.

* User-visible changes

  * Specifying --fq-rate or --no-fq-socket-pacing on a system where
    these options are not supported now generate an error instead of a
    warning.  This change makes diagnosing issues related to pacing
    more apparent.

  * Fixed a bug where two recently-added diagnostic messages spammed
    the JSON output on UDP tests.