Updated wlan with promoscious mode example

content/firmwareapi/pycom/network/wlan.md

@@ -291,6 +291,29 @@ Note:
 * Promiscuous mode should be enabled for Wifi packets types Events to be triggered
 * for changing wifi channel via `wlan.channel()` promiscuous mode should be enabled.
 
+Example using promoscious mode:
+
+```
+from network import WLAN
+import ubinascii
+
+def pack_cb(pack):
+    mac = bytearray(6)
+    pk = wlan.wifi_packet()
+    control = pk.data[0]
+    subtype = (0xF0 & control) >> 4
+    type = 0x0C & control
+    #print("Control:{}, subtype:{}, type:{}".format(control, subtype, type))
+    if subtype == 4:
+        for i in range (0,6):
+            mac[i] = pk.data[10 + i]
+        print ("Wifi Node with MAC: {}".format(ubinascii.hexlify(mac)))
+
+wlan = WLAN(mode=WLAN.STA, antenna=WLAN.EXT_ANT)
+wlan.callback(trigger=WLAN.EVENT_PKT_MGMT, handler=pack_cb)
+wlan.promiscuous(True)
+```
+
 ### wlan.events()
 
 This function will return an integer object as mask for triggered events.