net: fix build on old Linux kernels Thanks to Mike Beller for identifying the problem.
net: fix build on old Linux kernels
Thanks to Mike Beller for identifying the problem.

Fixes issue 1442.

R=bradfitz, bradfitzgo
CC=golang-dev
http://codereview.appspot.com/4102042

pombredanne/go-deleteme,gnanderson/go,apparentlymart/golang,tv42/old-go,gnanderson/go,ssrl/go,tv42/old-go,gnanderson/go,gnanderson/go,ssrl/go,ssrl/go,apparentlymart/golang,dsriram/golang,pombredanne/go-deleteme,tv42/old-go,dsriram/golang,ssrl/go,tv42/old-go,pombredanne/go-deleteme,apparentlymart/golang,apparentlymart/golang,tv42/old-go,tv42/old-go,gnanderson/go,pombredanne/go-deleteme,gnanderson/go,dsriram/golang,apparentlymart/golang,apparentlymart/golang,ssrl/go,pombredanne/go-deleteme,dsriram/golang,tv42/old-go,dsriram/golang,ssrl/go,dsriram/golang,apparentlymart/golang,pombredanne/go-deleteme,ssrl/go,pombredanne/go-deleteme,gnanderson/go,dsriram/golang