iwlwifi: build some station commands directly

In the powersave related functions we only need
to set a few parameters for the station command
and can otherwise leave it blank -- there's no
need to copy it from the database.

This allows us to not use the sta lock here.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>