It's possible to control the source address of a UDP packet by
passing a socket control message of type IP_PKTINFO or IPV6_PKTINFO.
This is a somewhat esoteric feature of the network stack, but it's
extremely useful feature when you really need it.
Change-Id: I8300575f975679f6689d6f1282af253ba62e8f9d
Reviewed-on: https://go-review.googlesource.com/c/sys/+/355610
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Trust: Tobias Klauser <tobias.klauser@gmail.com>