mac80211: add support for setting the ad-hoc multicast rate

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

diff --cc include/net/mac80211.h
Simple merge

diff --cc net/mac80211/ibss.c
Simple merge

diff --cc net/mac80211/rate.c
Simple merge

diff --cc net/mac80211/tx.c
Simple merge