Track the number of bad beacons received.

PR:		kern/165517

sys/net80211/ieee80211_ioctl.h

@@ -241,8 +241,9 @@ struct ieee80211_stats {
 	uint32_t	is_mesh_notproxy;	/* dropped 'cuz not proxying */
 	uint32_t	is_rx_badalign;		/* dropped 'cuz misaligned */
 	uint32_t	is_hwmp_proxy;		/* PREP for proxy route */
+	uint32_t	is_beacon_bad;		/* Number of bad beacons */
 	
-	uint32_t	is_spare[11];
+	uint32_t	is_spare[10];
 };
 
 /*

sys/net80211/ieee80211_sta.c

@@ -1305,8 +1305,10 @@ sta_recv_mgmt(struct ieee80211_node *ni, struct mbuf *m0,
 			return;
 		}
 		/* XXX probe response in sta mode when !scanning? */
-		if (ieee80211_parse_beacon(ni, m0, &scan) != 0)
+		if (ieee80211_parse_beacon(ni, m0, &scan) != 0) {
+			vap->iv_stats.is_beacon_bad++;
 			return;
+		}
 		/*
 		 * Count frame now that we know it's to be processed.
 		 */