carl9170: fix allmulticast mode

Currently, the driver only disable multicast filtering when the
FIF_ALLMULTI driver flag has been just set (ie,
if changed_flags& FIF_ALLMULTI and *new_flags& FIF_ALLMULTI) or else
it will reenable multicast filtering.

But next time, this condition will be false and multicast filtering
will be reenabled, even through FIF_ALLMULTI is still set.

This mean that allmulticast only works for less than two minutes in
ad-hoc mode.  This patch fixes that to disable multicast filtering
as long as FIF_ALLMULTI is set.
Signed-off-by: Nicolas Cavallari  <cavallar@lri.fr>
Acked-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/carl9170/main.c

@@ -883,7 +883,7 @@ static void carl9170_op_configure_filter(struct ieee80211_hw *hw,
 	 * then checking the error flags, later.
 	 */
 
-	if (changed_flags & FIF_ALLMULTI && *new_flags & FIF_ALLMULTI)
+	if (*new_flags & FIF_ALLMULTI)
 		multicast = ~0ULL;
 
 	if (multicast != ar->cur_mc_hash)