wifi: mac80211: Pull link space calculation to a function

Pull the calculation of the size needed for a link in an association
request frame to a function, so it could also be used during the
construction of other frames as well, e.g., ML link configuration
request frame.

Signed-off-by: Ilan Peer <ilan.peer@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20250102161730.ac16adfa39d4.I9e28c2fcd5ca252341c817fc03ea8df7b807fcbf@changeid


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