wifi: ieee80211: document function return values

These are all missing, as pointed out when running kernel-doc.
Add return value documentation and fix some small things while
at it.

Link: https://msgid.link/20240515093852.1cd5ad8f354d.Idc16e9767fa42de80b659c32efc58aea38c26996@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>