spidernet: revise link status logging

This patch revises the logging for link informations of spidernet.

  - The link down message is too verbose because auto-negotiation timeout
    occurs periodically while an ethernet cable is not connected.
  - We want to see the link result, and we think it should be displayed.

Signed-off-by: Kou Ishizaki <kou.ishizaki@toshiba.co.jp>
Acked-by: Jens Osterkamp <jens@de.ibm.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>