spidernet: increase auto-negotiation timeout to 5 seconds

This patch extends the timeout for spidernet auto-negotiation.
Auto-negotiation often fails to finish in 2 seconds.

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>