From: Shaun Jackman <sjackman@gmail.com>

This patch adds multicast filtering to the TUN network driver, for
packets being sent from the network device to the character device.

* drivers/net/tun.c: Add multicast filtering for packets travelling from
  the network device to the character device.

* include/linux/if_tun.h (tun_struct): Add interface flags, a hardware
  device addres, and a multicast filter.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>