iwlwifi: move wait_command_queue from shared to trans

This wait queue really belongs to the transport
layer, as it is used for sending synchronous
commands to the HW.

However, only op_mode knows about errors and
exceptional conditions, so make this queue
accessible by the op_mode.

Signed-off-by: Meenakshi Venkataraman <meenakshi.venkataraman@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>