mac80211: sample survey implementation for mac80211 & hwsim

This adds the survey function to both mac80211 itself and to mac80211_hwsim.
For the latter driver, we simply invent some noise level.A real driver which
cannot determine the real channel noise MUST NOT report any noise, especially
not a magically conjured one :-)

Signed-off-by: Holger Schurig <holgerschurig@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/mac80211/driver-ops.h b/net/mac80211/driver-ops.h
index c3d8440..d1f8a7c 100644
--- a/net/mac80211/driver-ops.h
+++ b/net/mac80211/driver-ops.h
@@ -346,6 +346,15 @@
 	return ret;
 }
 
+static inline int drv_get_survey(struct ieee80211_local *local, int idx,
+				struct survey_info *survey)
+{
+	int ret = -EOPNOTSUPP;
+	if (local->ops->conf_tx)
+		ret = local->ops->get_survey(&local->hw, idx, survey);
+	/* trace_drv_get_survey(local, idx, survey, ret); */
+	return ret;
+}
 
 static inline void drv_rfkill_poll(struct ieee80211_local *local)
 {