Staging: octeon-ethernet: Convert to use net_device_ops.

Convert the driver to use net_device_ops as it is now mandatory.

Also compensate for the removal of struct sk_buff's dst field.

The changes are mostly mechanical, the content of ethernet-common.c
was moved to ethernet.c and ethernet-common.{c,h} are removed.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>