iwlwifi: remove key information during device restart

When there is a firmware error or the firmware is reloaded for some other
reason we currently clear all station information, including keys
associated with them. A problem is that we do not clear some other
information regarding keys that are not stored in the station structs.

The consequence of this is that when the device is reconfigured after the
firmware reload we can, among other things, run out of key indices.

This fixes:
https://bugzilla.kernel.org/show_bug.cgi?id=16232
http://bugzilla.intellinuxwireless.org/show_bug.cgi?id=2221

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>