iwlagn: workaround bug crashing some APs

This patch reverts commit 9b7688328422b88a7a15dc0dc123ad9ab1a6e22d which
was introduced in 2.6.38-rc1.  It works around a problem where the iwlagn
driver stimulates a bug crashing (requiring power cycle to recover) some
APs under heavy traffic.

CC: stable@kernel.org #2.6.39, #3.0.0 #3.1.0
Signed-off-by: Don Fry <donald.h.fry@intel.com>
SIgned-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>