sunvnet: fix rx packet length check to allow for TSO

This patch fixes the rx packet length check in the sunvnet driver to allow
for a TSO max packet length greater than the LDC channel negotiated MTU.
These are negotiated separately and there is no requirement that
port->tsolen be less than port->rmtu, but if it isn't, it'll drop packets
with rx length errors.

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