net80211/regdomain: try to sort out TW

Try to help people in TW to get onto 11ac as well by adding the missing
entries to regdomain.xml. Use at your own risk.

regdomain.xml is unmaintanable in the modern world with too many tiny
difference between countries. We'll need a different way to generate
this or a different representation long term.

Sponsored by: The FreeBSD Foundation
Reported by: lwhsu
Tested by: lwhsu
Reviewed by: lwhsu, adrian
Differential Revision: https://reviews.freebsd.org/D49776

(cherry picked from commit 84e1eb50dd9529b234e568ccb6f6c37f897688dc)