sunvnet: Initialize network_header and transport_header in vnet_rx_one()

vnet_fullcsum() accesses ip_hdr() and transport header to compute
the checksum for IPv4 packets, so these need to be initialized in
skb created in vnet_rx_one().

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>