net/http: simplify serve() connection close
net/http: simplify serve() connection close

Followup to 6971049.

R=bradfitz
CC=golang-dev
https://codereview.appspot.com/6970049

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