cfg80211: allow per interface TX power setting

The TX power setting is currently per wiphy (hardware
device) but with multi-channel capabilities that doesn't
make much sense any more.

Allow drivers (and mac80211) to advertise support for
per-interface TX power configuration. When the TX power
is configured for the wiphy, the wdev will be NULL and
the driver can still handle that, but when a wdev is
given the TX power can be set only for that wdev now.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/include/uapi/linux/nl80211.h b/include/uapi/linux/nl80211.h
index 617d0fb..4c5f674 100644
--- a/include/uapi/linux/nl80211.h
+++ b/include/uapi/linux/nl80211.h
@@ -3051,6 +3051,7 @@
  * @NL80211_FEATURE_LOW_PRIORITY_SCAN: This driver supports low priority scan
  * @NL80211_FEATURE_SCAN_FLUSH: Scan flush is supported
  * @NL80211_FEATURE_AP_SCAN: Support scanning using an AP vif
+ * @NL80211_FEATURE_VIF_TXPOWER: The driver supports per-vif TX power setting
  */
 enum nl80211_feature_flags {
 	NL80211_FEATURE_SK_TX_STATUS			= 1 << 0,
@@ -3062,6 +3063,7 @@
 	NL80211_FEATURE_LOW_PRIORITY_SCAN		= 1 << 6,
 	NL80211_FEATURE_SCAN_FLUSH			= 1 << 7,
 	NL80211_FEATURE_AP_SCAN				= 1 << 8,
+	NL80211_FEATURE_VIF_TXPOWER			= 1 << 9,
 };
 
 /**