net: fix typo in failure message in test
net: fix typo in failure message in test

R=golang-dev, mikioh.mikioh
CC=golang-dev
https://codereview.appspot.com/14582043

pombredanne/go-deleteme,tv42/old-go,apparentlymart/golang,tv42/old-go,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,pombredanne/go-deleteme,apparentlymart/golang,tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,apparentlymart/golang,pombredanne/go-deleteme,apparentlymart/golang,pombredanne/go-deleteme,pombredanne/go-deleteme