net: no panic on placeholders for netbsd
net: no panic on placeholders for netbsd

Perhaps it might be better than panic.

R=golang-dev, r
CC=golang-dev
http://codereview.appspot.com/5701064
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go