[PATCH] zd1211rw: Added error stats update

Added update of network device error statistics.

Based on earlier work by Maxime Austruy.

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>