iwlwifi: improve station debugfs

The stations debugfs entry doesn't even show
the stations' MAC addresses Also, the TID
information is formatted very oddly, and
misses the important tfds_in_queue variable.
Fix this to make the file more useful.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>