mac80211: mesh: fix mesh path kerneldoc

Several of the mesh path fields are undocumented and some
of the documentation is no longer correct or relevant after
the switch to rhashtable.  Clean up the kernel doc
accordingly and reorder some fields to match the structure
layout.

Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>