release: Install wireless firmware to bootonly media
Also install wireless firmware packages to the bootonly ISO and the
mini-memstick image so users can fetch installation files over a
wireless connection.
Reported by: Mark Philips <mark@freebsdfoundation.org>
Reviewed by: bz, emaste, imp, releng (cperciva)
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D51348