mac80211: minstrel_ht: fix a logic error in RTS/CTS handling

commit c36dd3ea upstream.

RTS/CTS needs to be enabled if the rate is a fallback rate *or* if it's
a dual-stream rate and the sta is in dynamic SMPS mode.

Fixes: a3ebb4e1 ("mac80211: minstrel_ht: handle peers in dynamic SMPS")
Reported-by: Matías Richart <mrichart@fing.edu.uy>
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>