Be a bit more precisly in the description of the sysctl variable
net.inet.tcp.pmtud_blackhole_detection. Also remove three entries,
which are not sysctl variables but statistic counters for TCP.
Thanks to 0mp@ for suggesting an improvement.
Reviewed by: bcr@
Sponsored by: Netflix, Inc.
Differential Revision: https://reviews.freebsd.org/D24216