net: ethernet: sun: niu set correct packet size in skb

Currently, skb->len and skb->data_len are set to the page size, not
the packet size. This causes the frame check sequence to not be
located at the "end" of the packet resulting in ethernet frame check
errors. The driver does work currently, but stricter kernel facing
networking solutions like OpenVSwitch will drop these packets as
invalid.

These changes set the packet size correctly so that these errors no
longer occur. The length does not include the frame check sequence, so
that subtraction was removed.

Tested on Oracle/SUN Multithreaded 10-Gigabit Ethernet Network
Controller [108e:abcd] and validated in wireshark.

Signed-off-by: Rob Taglang <rob@taglang.io>
Signed-off-by: David S. Miller <davem@davemloft.net>