docs: private-wlan: add uci command to set MAC (#1454)

add a missing command to set the special Gluon MAC address of the private WLAN interface to the documentation.

docs/features/private-wlan.rst

@@ -7,14 +7,19 @@ Please note that you should not enable ``mesh_on_wan`` simultaneously.
 The private WLAN can be enabled through the config mode if the package ``gluon-web-private-wifi`` is installed.
 You may also enable a private WLAN using the command line::
 
-  uci set wireless.wan_radio0=wifi-iface
-  uci set wireless.wan_radio0.device=radio0
-  uci set wireless.wan_radio0.network=wan
-  uci set wireless.wan_radio0.mode=ap
-  uci set wireless.wan_radio0.encryption=psk2
-  uci set wireless.wan_radio0.ssid="$SSID"
-  uci set wireless.wan_radio0.key="$KEY"
-  uci set wireless.wan_radio0.disabled=0
+  RID=0
+  SSID="privateWLANname"
+  KEY="yoursecret1337password"
+
+  uci set wireless.wan_radio$RID=wifi-iface
+  uci set wireless.wan_radio$RID.device=radio$RID
+  uci set wireless.wan_radio$RID.network=wan
+  uci set wireless.wan_radio$RID.mode=ap
+  uci set wireless.wan_radio$RID.encryption=psk2
+  uci set wireless.wan_radio$RID.ssid="$SSID"
+  uci set wireless.wan_radio$RID.key="$KEY"
+  uci set wireless.wan_radio$RID.disabled=0
+  uci set wireless.wan_radio$RID.macaddr="$($(echo "lua -e print(require('gluon.util').generate_mac(3+4*$RID))"))"
   uci commit
   wifi