While IEEE80211_R_BAND was defined, there was no place to store the
band. Add a field for that, adjust ieee80211_lookup_channel_rxstatus()
to require it, and update drivers passing "R_{FREQ|IEEE}" in already to
provide the band as well. For the moment keep the fall-back code
requiring all three fields.
Sponsored by: The FreeBSD Foundation
(cherry picked from commit 9a6695532b)
