gluon-core: fall back to eth0 for the primary MAC address when there is no WLAN device

package/gluon-core/files/lib/gluon/upgrade/010-primary-mac

 #!/usr/bin/lua
 
 local sysconfig = require 'gluon.sysconfig'
+
+
+if sysconfig.primary_mac then
+  os.exit(0)
+end
+
+
 local platform = require 'gluon.platform'
 
 local fs = require 'luci.fs'
 local util = require 'luci.util'
 
 
-if not sysconfig.primary_mac then
-  if platform.match('ar71xx', 'generic', {'tl-wdr3600', 'tl-wdr4300'}) then
-    sysconfig.primary_mac = util.trim(fs.readfile('/sys/class/ieee80211/phy1/macaddress'))
-  else
-    sysconfig.primary_mac = util.trim(fs.readfile('/sys/class/ieee80211/phy0/macaddress'))
+local try_files = {
+  '/sys/class/ieee80211/phy0/macaddress',
+  '/sys/class/net/eth0/address',
+}
+
+if platform.match('ar71xx', 'generic', {'tl-wdr3600', 'tl-wdr4300'}) then
+  table.insert(try_files, 1, '/sys/class/ieee80211/phy1/macaddress')
+end
+
+
+for _, file in ipairs(try_files) do
+  local addr = fs.readfile(file)
+
+  if addr then
+    sysconfig.primary_mac = util.trim(addr)
+    break
   end
 end