mac80211: convert HW flags to unsigned long bitmap

As we're running out of hardware capability flags pretty quickly,
convert them to use the regular test_bit() style unsigned long
bitmaps.

This introduces a number of helper functions/macros to set and to
test the bits, along with new debugfs code.

The occurrences of an explicit __clear_bit() are intentional, the
drivers were never supposed to change their supported bits on the
fly. We should investigate changing this to be a per-frame flag.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

drivers/net/wireless/at76c50x-usb.c

@@ -2360,8 +2360,8 @@ static int at76_init_new_device(struct at76_priv *priv,
 	priv->hw->wiphy->max_scan_ie_len = 0;
 	priv->hw->wiphy->interface_modes = BIT(NL80211_IFTYPE_STATION);
 	priv->hw->wiphy->bands[IEEE80211_BAND_2GHZ] = &at76_supported_band;
-	priv->hw->flags = IEEE80211_HW_RX_INCLUDES_FCS |
-			  IEEE80211_HW_SIGNAL_UNSPEC;
+	ieee80211_hw_set(priv->hw, RX_INCLUDES_FCS);
+	ieee80211_hw_set(priv->hw, SIGNAL_UNSPEC);
 	priv->hw->max_signal = 100;
 
 	SET_IEEE80211_DEV(priv->hw, &interface->dev);