spidernet: compile break.

As of 2.6.20-git4, the spider_net driver does not compile.
This appears to be due to some archaic usage involving kobjects.

It also fixes a nasty double-free during ifdown of the interface.

Signed-off-by: Linas Vepstas <linas@austin.ibm.com>
Cc: Jens Osterkamp <Jens.Osterkamp@de.ibm.com>
Cc: Kou Ishizaki <kou.ishizaki@toshiba.co.jp>
Signed-off-by: Jeff Garzik <jeff@garzik.org>