iwlagn: work around rate scaling reset delay

When station is using an HT channel to communicate to AP and communication
is lost then driver will first be notified that channel is not an HT
channel anymore before AP station is removed. A consequence of that is that
the driver will know that it is not communicating on HT anymore, but the
rate scaling table is still under the impression it is operating in HT. Any
time after driver has been notified channel is not HT anymore there will
thus be a firmware SYSASSERT when the current active LQ command is sent.

A workaround for this issue is to not send a LQ command in the short time between
being notified channel is not HT anymore and rate scaling table being
updated.

This fixes http://bugzilla.intellinuxwireless.org/show_bug.cgi?id=2173



Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>