measurement: add handling of measurements

Add logic for saving measurement-reports from STAs.

This commit does not yet save the measurement-reports received from
clients but adds the necessary code to do so. Currently the codes can
only handle beacon-reports, but link measurements can be added to it in
the future.

It also adds the new config-key measurement_report_timeout which
controls how long measurements are saved upon they are received by a
STA.

Signed-off-by: David Bauer <mail@david-bauer.net>

sta.c

@@ -35,6 +35,7 @@ usteer_sta_del(struct sta *sta)
 	    MAC_ADDR_DATA(sta->addr));
 
 	avl_delete(&stations, &sta->avl);
+	usteer_measurement_report_sta_cleanup(sta);
 	free(sta);
 }
 
@@ -140,6 +141,7 @@ usteer_sta_get(const uint8_t *addr, bool create)
 	sta->avl.key = sta->addr;
 	avl_insert(&stations, &sta->avl);
 	INIT_LIST_HEAD(&sta->nodes);
+	INIT_LIST_HEAD(&sta->measurements);
 
 	return sta;
 }