net: Don't use stack space for fd_sets when using select.
net: Don't use stack space for fd_sets when using select.

PR go/59433

R=iant
CC=gofrontend-dev
https://golang.org/cl/48750045

anlhord/gofrontend,golang/gofrontend,anlhord/gofrontend,qskycolor/gofrontend,qskycolor/gofrontend,qskycolor/gofrontend,anlhord/gofrontend,golang/gofrontend,anlhord/gofrontend,qskycolor/gofrontend,qskycolor/gofrontend,anlhord/gofrontend,anlhord/gofrontend,golang/gofrontend,anlhord/gofrontend,golang/gofrontend,qskycolor/gofrontend,qskycolor/gofrontend