gluon-core: only restore WAN proto on upgrade (#2576)

Only restore the netifd proto for the WAN bridge in case the upgrade is
done from an older Gluon version.

For DSL targets, OpenWrt defaults the WAN proto to pppoe, while Gluon
uses the Ethernet ports for WAN. When unconditionally preserving the WAN
proto, pppoe is carried over to Gluon's network config.

Signed-off-by: David Bauer <mail@david-bauer.net>

package/gluon-core/luasrc/lib/gluon/upgrade/110-network

 #!/usr/bin/lua
 
 local uci = require('simple-uci').cursor()
+
+local sysconfig = require 'gluon.sysconfig'
 local util = require 'gluon.util'
 
 local wan = uci:get_all('network_gluon-old', 'wan') or {}
@@ -13,8 +15,15 @@ uci:section('network', 'interface', 'loopback', {
 	netmask = '255.0.0.0',
 })
 
+local wan_proto = 'dhcp'
+
+if sysconfig.gluon_version and wan.proto ~= nil then
+	-- Only restore WAN proto in case this is an upgrade
+	wan_proto = wan.proto
+end
+
 uci:section('network', 'interface', 'wan', {
-	proto = wan.proto or 'dhcp',
+	proto = wan_proto,
 	ipaddr = wan.ipaddr,
 	netmask = wan.netmask,
 	gateway = wan.gateway,