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/drivers/net/wireless/mwifiex/cfg80211.c b/drivers/net/wireless/mwifiex/cfg80211.c
index fdb1eb8..8e829b2 100644
--- a/drivers/net/wireless/mwifiex/cfg80211.c
+++ b/drivers/net/wireless/mwifiex/cfg80211.c
@@ -324,6 +324,7 @@
  */
 static int
 mwifiex_cfg80211_set_tx_power(struct wiphy *wiphy,
+			      struct wireless_dev *wdev,
 			      enum nl80211_tx_power_setting type,
 			      int mbm)
 {