iwlwifi: Complete backport of "iwlwifi: always copy first 16 bytes of commands"

iwlwifi: Complete backport of "iwlwifi: always copy first 16 bytes of commands"

Linux 3.4.83 included an incomplete backport of commit
8a964f44e01ad3bbc208c3e80d931ba91b9ea786 ('iwlwifi: always copy first
16 bytes of commands') which causes a regression for this driver.
This is the missing piece.

Reported-by: Andreas Sturmlechner <andreas.sturmlechner@gmail.com>
Cc: Johannes Berg <johannes.berg@intel.com>
Cc: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Cc: Jianguo Wu <wujianguo@huawei.com>
Cc: Andres Bertens <abertensu@yahoo.com>
Tested-by: Andreas Sturmlechner <andreas.sturmlechner@gmail.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>