patch b3316157 in mainline.

In STA mode, the AP will echo our traffic.  This includes multicast
traffic.

Receiving these frames confuses some protocols and applications,
notably IPv6 Duplicate Address Detection.
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Michael Wu <flamingice@sourmilk.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>