prometheus-node-exporter-lua: an unavaliable wifi interface may have stopped the scraper from functioning

Signed-off-by: Zoltan Haindrich <kirk@rxd.hu>
(cherry picked from commit 7bec619f53)

utils/prometheus-node-exporter-lua/files/usr/lib/lua/prometheus-collectors/wifi.lua

@@ -13,6 +13,7 @@ local function scrape()
   for dev, dev_table in pairs(status) do
     for _, intf in ipairs(dev_table['interfaces']) do
       local ifname = intf['ifname']
+      if ifname ~= nil then
         local iw = iwinfo[iwinfo.type(ifname)]
         local labels = {
           channel = iw.channel(ifname),
@@ -38,6 +39,7 @@ local function scrape()
         metric_wifi_network_signal(labels, iw.signal(ifname) or -255)
       end
     end
+  end
 end
 
 return { scrape = scrape }

utils/prometheus-node-exporter-lua/files/usr/lib/lua/prometheus-collectors/wifi_stations.lua

@@ -26,6 +26,7 @@ local function scrape()
   for dev, dev_table in pairs(status) do
     for _, intf in ipairs(dev_table['interfaces']) do
       local ifname = intf['ifname']
+      if ifname ~= nil then
         local iw = iwinfo[iwinfo.type(ifname)]
         local count = 0
 
@@ -64,6 +65,7 @@ local function scrape()
         metric_wifi_stations({ifname = ifname}, count)
       end
     end
+  end
 end
 
 return { scrape = scrape }