perfdhcp does not print all the RTT stats on no received packets
When there are no received packets, an exception is thrown in
ExchangeStats::getAvgDelay() which results in
avg delay displayed like so:
min delay: inf ms avg delay: Delay summary unavailable! No packets received.
collected packets are missing.
Either display all or display none for easier automated parsing. I prefer displaying all. In that case, delays could get zero or inf values as they are impossible values. Or sure, display an error message.