net/rpc: fix build
net/rpc: fix build

LGTM=adg
R=golang-codereviews, adg
CC=golang-codereviews
https://codereview.appspot.com/151620043

tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go