[release-branch.go1.2] net: ignore some errors in windows Accept

««« CL 49490043 / 7ecbc2b8ec97
net: ignore some errors in windows Accept

Fixes #6987

R=golang-codereviews, dvyukov
CC=golang-codereviews
https://golang.org/cl/49490043
»»»

LGTM=r
R=golang-codereviews, r
CC=golang-dev
https://golang.org/cl/69780044