virtio-net support

This adds virtio-net support.  This is based on the virtio-net driver 
that exists in kvm-userspace.  This also adds a new qemu_sendv_packet 
which virtio-net requires.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6073 c046a42c-6fe2-441c-8c8c-71466251a162