mac80211: add a flag to indicate CCK support for HT clients

commit 2dfca312 upstream.

brcm80211 cannot handle sending frames with CCK rates as part of an
A-MPDU session. Other drivers may have issues too. Set the flag in all
drivers that have been tested with CCK rates.

This fixes a reported brcmsmac regression introduced in
commit ef47a5e4
"mac80211/minstrel_ht: fix cck rate sampling"

Reported-by: Tom Gundersen <teg@jklm.no>
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>