[PATCH] zd1211rw: Added workqueue

For housekeeping and watchdog tasks a workqueue is created. The
central workqueue is not used to prevent crashes creates by bugs.
It might be changed, when the housekeeping is stabilized.

Signed-off-by: Ulrich Kunitz <kune@deine-taler.de>
Signed-off-by: Daniel Drake <dsd@gentoo.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>