wifi: mac80211: rename ieee80211_ie_build_he_6ghz_cap()

The term 'IE' isn't really in use in the spec, and I want
to rework all of this to use SKBs as the primary method
for building elements. Rename this one already.

Link: https://msgid.link/20240129202041.b8064a4e73b5.I8d2f4526562029107c6414c6cda378b300b1b0b0@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>