Fix the problem that can not delete the udp socket.
It's caused by passing "udp" model to net_socket_udp_init,
but we do not have "udp" model in our model list.
Pass the right model "socket" to init function.
https://bugs.launchpad.net/qemu/+bug/1073585?comments=all
Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>