iwlwifi: fixed testmode notifications length

The length of iwl_rx_packet doesn't include the
dword for the length itself, so add it manually.

Signed-off-by: Amit Beka <amit.beka@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>