virtio-net: add vlan receive state to RxFilterInfo

virtio-net: add vlan receive state to RxFilterInfo

Stefan Fritsch just fixed a virtio-net driver bug [1], virtio-net won't
filter out VLAN-tagged packets if VIRTIO_NET_F_CTRL_VLAN isn't negotiated.

This patch added a new field to @RxFilterInfo to indicate vlan receive
state ('normal', 'none', 'all'). If VIRTIO_NET_F_CTRL_VLAN isn't
negotiated, vlan receive state will be 'all', then all VLAN-tagged packets
will be received by guest.

This patch also fixed a boundary issue in visiting vlan table.

[1] http://lists.nongnu.org/archive/html/qemu-devel/2014-02/msg02604.html

Signed-off-by: Amos Kong <akong@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>