Add missing sg_init_table for sg_set_buf in virtio_net which
induced in defer skb patch.
Reported-by: Thomas Müller <thomas@mathtm.de> Tested-by: Thomas Müller <thomas@mathtm.de> Signed-off-by: Shirley Ma <xma@us.ibm.com> Signed-off-by: David S. Miller <davem@davemloft.net>