net80211: simplify code after STA/AP VAPs traffic hang fix

Combine the comment and double-unsetting of OACTIVE into a single case
after e8de31caceaa36caf5d7b4355072f148e2433b82.
This saves the question of why we do it twice--once right before and
one more time right after the state change check.
Also move the XXX comment about kicking the queue up to where it seems
better suited now.

Sponsored by: The FreeBSD Foundation
Reviewed by: adrian
Differential Revision: https://reviews.freebsd.org/D35135

(cherry picked from commit 464907ce1cf931091fa48999ea64480a6d2ef52c)