The packet_mreq structure is used on Linux to modify the behavior
of packet sockets using setsockopt.  See 'man 7 packet' for more
details.

Change-Id: I34e5b99a6b6eb1f23d49a9c9f25ce7b77121c8f0
Reviewed-on: https://go-review.googlesource.com/51710
Run-TryBot: Matt Layher <mdlayher@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>