The intent is to skip expensive sysctls like tcp_pcblist unless
they are explicitly asked for. These opaqueue sysctls don't show
up in sysctl -a, but they do generate output that winds up being
just dropped by sysctl, unless the user specifically asked to
see binary/hex output or opaques.

On a loaded system, this reduces the time to run
sysctl -a by a factor of 4 or so:

c059.ord001.dev# /usr/bin/time /sbin/sysctl -a > /dev/null

0.17 real         0.01 user         0.11 sys

c059.ord001.dev# /usr/bin/time /sbin/sysctl.old -a > /dev/null

0.75 real         0.01 user         0.50 sys

(and a factor of 2 or so on an unloaded system)

Unintentionally requesting some of these opaque sysctls
when debugging a sick machine can be enough to push things
over the edge sometimes.