undo CL 5687057 / 58bc8aae4abb

Fortunately we have never seen the panic on sockaddrToTCP
in the past year.

??? original CL description
net: panic if sockaddrToTCP returns nil incorrectly
Part of diagnosing the selfConnect bug
TBR=dsymonds

R=golang-dev
CC=golang-dev
http://codereview.appspot.com/5687057
???

R=golang-dev, minux.ma
CC=golang-dev
https://codereview.appspot.com/7137063