net80211: fix VHT node setup in hostap mode

Way back in 2017 I wrote the initial VHT hostap support, and then
added a NULL check here to stop it from panicing. However, there
is no VHTINFO IE in an ASSOC_REQ management frame. Thus, the node
would never have VHT state initialised.

This mirrors what HT node setup does (which again doesn't have
HTINFO IE's in an ASSOC_REQ frame), the upgrade will happen once
the exchange completes.

Fixes: 2023566223a4020d832bd4e25dc7dadfd660b836
Differential Revision: https://reviews.freebsd.org/D50787