net: don't return a nested error when happy eyeballs dialing
net: don't return a nested error when happy eyeballs dialing

Also removes an unused variable.

Fixes issue 6795.

R=adg, dave, bradfitz, gobot
CC=golang-dev
https://codereview.appspot.com/29440043

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