iwlwifi: dbg: move trans debug fields to a separate struct

Unite iwl_trans debug related fields under iwl_trans_debug struct to
increase readability and keep iwl_trans clean.

Signed-off-by: Shahar S Matityahu <shahar.s.matityahu@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>