At ifup, carrier status would be shown on even if it actually was off.
Also add an include for ethtool_ops rather than to rely on the one from
netdevice.h.

Note, we can alas not use fwnet_device_mutex to serialize access to
dev->peer_count (as I originally wanted).  This would cause a lock
inversion:
  - fwnet_probe | takes fwnet_device_mutex
      + register_netdev | takes rtnl_mutex
  - devinet_ioctl | takes rtnl_mutex
      + fwnet_open | ...must not take fwnet_device_mutex

Hence use the dev->lock spinlock for serialization.
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>