net80211: sta: RUN to INIT is a DEAUTH not a DISASSOC

[bz]

Summary

When taking a node down from RUN to INIT (the latter being the important
part) we are going back to State 1 (cf. 802.11-2024, Figure 11-23) and
that is a DEUATH and not a DISASSOC change (like ASSOC to INIT).
Correct the management type frame we are sending and reason.

Sponsored by: The FreeBSD Foundation
MFC after: 3 days

Test Plan

Is there any reason why we did send a disassoc in this case forever?
I saw it elsewhere too in a Linux based product which made me wonder.
Even the simple diagram in 802.11-2007 (Figure 11-6) seems to have
it as deauth.