net: fix TestDialFailPDLeak to work when GOMAXPROCS is large
net: fix TestDialFailPDLeak to work when GOMAXPROCS is large

Fixes issue 6553.

R=golang-dev, mikioh.mikioh
CC=golang-dev
https://codereview.appspot.com/14526048

wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,wesolows/golang,wesolows/golang,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,wesolows/golang,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang