This CL changes default SOL_SOCKET settings to mitigate connect
failure on OpenBSD or similar platforms which support randomized
transport protocol port number assignment.
Fixes#2830.
R=rsc, jsing
CC=golang-dev
https://golang.org/cl/5648044
This CL introduces new function ListenMulticastUDP to fix
multicast UDP listening across multiple listeners issue,
to replace old multicast methods JoinGroup and LeaveGroup
on UDPConn.
This CL also enables multicast testing by default.
Fixes#2730.
R=rsc, paul.a.lalonde, fullung, devon.odell
CC=golang-dev
https://golang.org/cl/5562048