perf/lat/stdev

r314268
https://lists.freebsd.org/pipermail/freebsd-net/2017-January/047073.html  Feb 25th.
719bf70a37139bc3bedc84ab0975df7107155714
Linux centos7 3.10.0-514.6.2.el7.x86_64
Linux deb 4.9.0-1-amd64

fbsd 77916.71 121ms 204ms
solisten 26240.37 294ms 248ms
linux3 178901.19 113ms 277ms
linux4 205106.83 129ms 302ms
dfly 207323.29 48ms 63ms
dfly-nodebug 219216.27 41ms 47ms

8K
fbsd 77803.72 121ms 230ms
solisten 25968.87 251ms 226ms
linux3 174017.76 117ms 298ms
linux4 176737.50 135ms 306ms
dfly 180750.19 53ms 60ms
dfly-nodebug 193381.64 49ms 53ms

16K
fbsd 75698.77 173ms 233ms
solisten 25047.23 377ms 246ms
linux3 132413.82 130ms 305ms
linux4 136867.44 145ms 314ms
dfly 136955.33 140ms 59ms
dfly-nodebug 137979.23 183ms 59ms