cfg80211: add 6GHz in code handling array with NUM_NL80211_BANDS entries

In nl80211.c there is a policy for all bands in NUM_NL80211_BANDS and
in trace.h there is a callback trace for multicast rates which is per
band in NUM_NL80211_BANDS. Both need to be extended for the new
NL80211_BAND_6GHZ.

Reviewed-by: Pieter-Paul Giesberts <pieter-paul.giesberts@broadcom.com>
Reviewed-by: Leon Zegers <leon.zegers@broadcom.com>
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Link: https://lore.kernel.org/r/1564745465-21234-6-git-send-email-arend.vanspriel@broadcom.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>