Generic netlink is a generalized netlink family which enables a series
of different communication channels to be multiplexed on a single
netlink family.

For more information, please see: https://lwn.net/Articles/208755/.

Fixes golang/go#21682.

Change-Id: I2095150e06471f4a0e1322fba669573aa8f0a9b1
Reviewed-on: https://go-review.googlesource.com/59931
Run-TryBot: Matt Layher <mdlayher@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>