iwlwifi: trans: use a unified transport status

The same bits are employed in all transport layers. Put the status
field in the common transport layer. This allows us to employ them
in common transport code.

Signed-off-by: Arik Nemtsov <arik@wizery.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>