LinuxKPI 802.11 / iwlwifi / rtw88 : re-factor ieee802211_sta for MLO

Working on an update for rtw88 baed on wireless-testing I ran into
a build issue with struct ieee802211_sta. Some fields were factored
out into their own struct apparently preparing for MLO (Multi Link
Operation).

In order to be able to update one driver we have to adjust both
rtw88 and iwlwifi (and the ones still out-of-tree) now.

This is mostly a sed-replace job and no functional changes are
intended.

Sponsored by: The FreeBSD Foundation
MFC after: 3 days