cfg80211: fix NAN bands definition

The nl80211_nan_dual_band_conf enumeration doesn't make much sense.
The default value is assigned to a bit, which makes it weird if the
default bit and other bits are set at the same time.

To improve this, get rid of NL80211_NAN_BAND_DEFAULT and add a wiphy
configuration to let the drivers define which bands are supported.
This is exposed to the userspace, which then can make a decision on
which band(s) to use.  Additionally, rename all "dual_band" elements
to "bands", to make things clearer.

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/wireless/core.c b/net/wireless/core.c
index 903fc419..e55e05b 100644
--- a/net/wireless/core.c
+++ b/net/wireless/core.c
@@ -626,7 +626,8 @@
 
 	if (WARN_ON((wiphy->interface_modes & BIT(NL80211_IFTYPE_NAN)) &&
 		    (!rdev->ops->start_nan || !rdev->ops->stop_nan ||
-		     !rdev->ops->add_nan_func || !rdev->ops->del_nan_func)))
+		     !rdev->ops->add_nan_func || !rdev->ops->del_nan_func ||
+		     !(wiphy->nan_supported_bands & BIT(NL80211_BAND_2GHZ)))))
 		return -EINVAL;
 
 #ifndef CONFIG_WIRELESS_WDS