mac80211: allow configure_filter callback to sleep

Over time, a whole bunch of drivers have come up
with their own scheme to delay the configure_filter
operation to a workqueue. To be able to simplify
things, allow configure_filter to sleep, and add
a new prepare_multicast callback that drivers that
need the multicast address list implement. This new
callback must be atomic, but most drivers either
don't care or just calculate a hash which can be
done atomically and then uploaded to the hardware
non-atomically.

A cursory look suggests that at76c50x-usb, ar9170,
mwl8k (which is actually very broken now), rt2x00,
wl1251, wl1271 and zd1211 should make use of this
new capability.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/at76c50x-usb.c

@@ -1997,15 +1997,14 @@ static void at76_bss_info_changed(struct ieee80211_hw *hw,
 /* must be atomic */
 static void at76_configure_filter(struct ieee80211_hw *hw,
 				  unsigned int changed_flags,
-				  unsigned int *total_flags, int mc_count,
-				  struct dev_addr_list *mc_list)
+				  unsigned int *total_flags, u64 multicast)
 {
 	struct at76_priv *priv = hw->priv;
 	int flags;
 
 	at76_dbg(DBG_MAC80211, "%s(): changed_flags=0x%08x "
-		 "total_flags=0x%08x mc_count=%d",
-		 __func__, changed_flags, *total_flags, mc_count);
+		 "total_flags=0x%08x",
+		 __func__, changed_flags, *total_flags);
 
 	flags = changed_flags & AT76_SUPPORTED_FILTERS;
 	*total_flags = AT76_SUPPORTED_FILTERS;