We should pass the size of packet instead of the remaining to
qemu_send_packet_async().

Fixes: 6e99c631
       ("net/socket: Drop net_socket_can_send")

Signed-off-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Message-id: 1436259656-24263-1-git-send-email-jasowang@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>