iwlagn: transport layer receives struct iwl_trans*

It still holds a pointer to iwl_priv. But hopefully this will disappear at some point.
Also add the multiple inclusion protection to iwl-trans.h that was forgotten.
Move iwl-trans structures to iwl-trans.h

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>