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/include/net/mac80211.h b/include/net/mac80211.h
index 63e9d37..cd99156 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -1674,7 +1674,8 @@
 			    struct ieee80211_vif *vif,
 			    enum ieee80211_ampdu_mlme_action action,
 			    struct ieee80211_sta *sta, u16 tid, u16 *ssn);
-
+	int (*get_survey)(struct ieee80211_hw *hw, int idx,
+		struct survey_info *survey);
 	void (*rfkill_poll)(struct ieee80211_hw *hw);
 	void (*set_coverage_class)(struct ieee80211_hw *hw, u8 coverage_class);
 #ifdef CONFIG_NL80211_TESTMODE