LinuxKPI: 802.11 updates

Add more values to the ieee80211_min_mpdu_start_spacing enum with
two missing given we do not know how they are called. Also update
the reference while here.

Add struct ieee80211_hdr_3addr and correct the comment on the
ieee80211_hdr to match the one in net80211 to avoid future confusion.

Sponsored by: The FreeBSD Foundation
MFC after: 3 days