tap: import linux multiqueue constants

tap: import linux multiqueue constants

Import multiqueue constants from if_tun.h from 3.8-rc3. A new ifr flag
IFF_MULTI_QUEUE were introduced to create a multiqueue backend by calling
TUNSETIFF with the this flag and with the same interface name many times.

A new ioctl TUNSETQUEUE were introduced. When doing this ioctl with
IFF_DETACH_QUEUE, the queue were disabled in the linux kernel. When doing this
ioctl with IFF_ATTACH_QUEUE, the queue were enabled in the linux kernel.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>